Part 72

To go back to the pock: some time before the contents of the marginal elevation become opaque the central portion is converted into a crust of a brownish color, and finally, from the tenth to the fifteenth day, the bourrelet itself, having ceased to increase in size, takes part in the process of incrustation, the completed crust representing the form of the pock, having a circular ridge at the border, at which part its color is not so deep as at the centre. The crust usually falls off between the fifteenth and the thirty-fifth day. It is hard, translucent, and of a prune-juice color; thick at the centre and thin at the periphery; smooth on its attached surface and somewhat wrinkled on its outer aspect; surmounted at the centre by the epidermal débris produced by the operation of inoculation, mingled perhaps with more or less dried blood.

After the crust falls off a reddened surface is left of a cicatricial nature, usually somewhat depressed below the level of the surrounding skin, and frequently showing lesser pits, which latter appearance is termed foveolation. Instead of these pits, radiated striæ are frequently left. Gradually the scar loses its red color, and, like other scars, finally becomes paler than the surrounding skin. It is usually permanent.

IRREGULARITIES IN THE COURSE OF THE DISEASE.--Ever since cow-pox first became the subject of medical study deviations from its typical course have been noticed, and have been the theme of a good deal of speculation. The older writers, indeed, bestowed no little attention upon what they considered to be not irregular forms of vaccinia, but distinct affections with which it was liable to be confounded. Their descriptions of these diseases, which they termed spurious cow-pox, are, however, so vague as to possess but little more than an historical interest. In regard to affections met with casually in the cow, we can often determine their nature only by test-inoculations, and even that criterion is not always thoroughly convincing; for, on one account or another, we may fail in the attempt to propagate true cow-pox, and on the other hand, if we admit that there is a radical difference between cow-pox and small-pox, it is manifest, bearing in mind the errors into which experienced investigators have fallen, that we may propagate small-pox through a long series of experiments without once suspecting it to be anything but cow-pox. We may, nevertheless, always determine, provided we succeed at all, whether we are dealing with a disease that protects against vaccinal and variolous inoculation.

In the human subject we seldom meet with affections that counterfeit vaccinia, although, if we take only the lesion into consideration, there are certain contagious forms of herpes that may give rise to doubt, and possibly the same may be true of impetigo contagiosa.

Turning, then, to the irregularities properly so called, we have first to consider the absence of constitutional infection. This must not be confounded with the mere lack of obvious constitutional symptoms; what is meant by the expression is, that in certain instances the local lesion may appear typical, and yet no such impression be made upon the system as to render it proof against subsequent inoculation. Early in the {461} century the possibility of this lack of systemic infection was insisted upon by Mr. Bryce of Edinburgh, who invoked it as an explanation of the occasional failure of vaccinia to protect against small-pox. The practical question was, how to decide, in a given instance, whether general infection had or had not taken place. In the opinion of many observers--and that notion has cropped out every now and then up to the present day--absence of the areola furnished at least presumptive evidence that the constitution had eluded infection. But, whatever may be held theoretically, it must be conceded either that the general system very rarely fails to feel the impress of the disease, or else that the criterion is fallacious. For in an experience of seventeen years the present writer has not known of a single instance in which a vaccinal lesion that pursued a regular course in other respects has failed to be accompanied by the areola. And certainly Mr. Bryce himself must have attached little if any importance to it, for he took great pains to establish a means of determining the presence or absence of constitutional infection--the so-called Bryce's test. This consists in repeating the inoculation at a certain period in the evolution of the disease, the theory being that systemic infection does not take place at once, but only after the lapse of a number of days from the time of the inoculation. Up to that time a repetition of the inoculation is possible, and, if systemic infection results from the first one, both lesions will mature at the same time, the second one following an accelerated course, reaching its acme rapidly, although dwarfed in size. If, on the other hand, the first inoculation failed to infect the constitution, the second one will pursue its course in the usual manner. Moreover, at a certain time, generally about the fifth day, a repetition of the inoculation will fail altogether if the original insertion has really infected the system. The present writer can testify that Mr. Bryce's statements are correct; he has applied the test in many cases, but in no instance has he been led to the conclusion that constitutional infection had failed to take place. He is inclined to think, therefore, that such failure is exceedingly rare.

Passing over the multiplicity of irregularities in the lesion that were described by the older observers, it seems that there are a few that are of practical importance. In the first place, there is a variety of pock to which it is not easy to give a definite name, but which is characterized by a lack of decided elevation above the surrounding skin (a deficiency for which it makes up in superficial area), by the early formation of a thin, flimsy, straw-colored crust, and by the utter failure of the characteristic firm brown crust of the typical variety to become developed. This form of irregular pock has not been seen by the writer of late years, but before animal vaccination came into general use he met with it frequently, mostly in cachectic children. Notwithstanding its sprawly, unsatisfactory appearance, it is undoubtedly genuine, for the typical lesion may be produced by inoculation with its contents.

Another irregularity of the pock is what is familiarly termed the raspberry excrescence. A red elevation forms at the seat of inoculation, and at first promises to follow the typical course, although it may be tardy in making it appearance; but it never advances to full development. It becomes indolent, and may last for several weeks, or even months, in the form of a hard, flat nodule of a bright-red color, not unlike a small {462} nævus. In many instances it has a succulent look, but no lymph can be obtained on puncturing it. No areola appears at any time, and finally the lesion slowly disappears, leaving no trace of its existence. It is probably an abortive form of pock, in which only the papillary layer of the skin takes part, without any exudation into the epidermis. It is seldom, if ever, protective against small-pox, for it constitutes no bar to a subsequent vaccination. This irregular pock has been observed from time to time ever since the early days of vaccination, but for the past six years it has been seen more frequently in New York than for many years before. Now, however, it seems to be growing less common. The writer is not aware of any satisfactory explanation of its occurrence. It is seen in all sorts of subjects, and seems to follow the use of one variety of virus as much as the employment of any other.

What has been termed generalized vaccinia is another form of irregularity. The expression is a vague one, covering as it does not only the very rare cases of true eruptive vaccinia, in which a general eruption of pocks takes place as a consequence of constitutional infection, playing the part of an exanthem, but in addition those instances, not very uncommon, in which pocks are formed here and there on the body, probably as the result of the accidental transfer of the virus from the pock by scratching. Under such favorable conditions--the immediate transfer of lymph from a pock in which the specific evolution is going on vigorously--the slightest penetration of the epidermis with the nails is enough to secure self-inoculation. In view of this facility with which it may be effected, we should be very careful not to jump hastily to the conclusion that in any given case of generalized vaccinia the supplementary pocks are truly eruptive; as a matter of fact, the present writer has never seen an instance in which he was convinced that such was the case. Where the pocks are very numerous, especially in subjects with an irritable skin, much distress may be caused by the itching and by the consequences of scratching, and marked febrile reaction may accompany the process; so that, in view of the great similarity of the lesions to those of the variolous eruption, much doubt is sometimes entertained as to whether the disease is not really small-pox. This question cannot always be definitely settled at first, but the failure of the secondary fever of small-pox, together with the fact that the disease does not spread by infection, will generally suffice to decide it.

Concerning those cases of generalized vaccinia that are manifestly not eruptive, it sometimes happens that the cutaneous receptivity is not exhausted for several weeks, or even months. Such cases set Bryce's test at defiance, in consequence, probably, of an idiosyncrasy. In some of these instances the pocks appear in clusters of successive formation, looking not unlike patches of zoster. Small supplementary pocks in the immediate neighborhood of the original lesion are not at all uncommon.

PATHOLOGICAL ANATOMY.--Avoiding the minute histological details for which the prescribed length of this article gives no scope, but little is to be added to what has already been said in the section on the clinical features of the disease. The lesions of vaccinia are wholly cutaneous. Confining ourselves to cases that follow a regular course, there is, indeed, but one, the pock--a term that seems preferable to vesicle and {463} pustule, since the latter apply only during certain phases in the development of the lesion.

A pock may be regarded as essentially a lesion of the epidermis, for it is in that structure that its most striking features are developed, and in some cases, although doubtless the papillary layer of the derma is congested, there is no permanent alteration of tissue below the Malpighian layer of the epidermis. These are the catarrhal pocks of Rindfleisch, and it is in such cases, if in any, that no scar (even of temporary duration) results. The term catarrhal pock, however, is not vitiated by an extension of the morbid process deep enough to produce a permanent cicatrix, and it is probable that in most cases the catarrhal type predominates. By the term diphtheritic pock the same author refers to cases in which the congestion of the papillary layer is so intense as to block the supply of blood to the apices of the papillæ, as a result of which they become exsanguinated and necrosed, forming a white pultaceous layer on the floor of the pock, which is undoubtedly what Ceely referred to when he spoke of a false membrane. In some cases even the subcutaneous tissue undergoes necrosis, a sort of core being included in the substance of the crust that ultimately forms.

Whichever of these forms of pock we take into consideration, always excluding irregularities and complications, we find certain definite changes in the epidermis. The dome of the pock is formed by the unbroken transparent horny layer of the epidermis, unaffected by the morbid process. The cavity of the pock is formed by the squamous cells of the epidermis being forced out of their normal relations by an exudation of lymph between them, some of them being tilted up edgewise while still retaining their connection with the surrounding cells, thus accounting for the multilocular structure of the pock; for it is a fact that the circular bourrelet consists not of one ring-like cavity, but of many separate chambers. The result of this structure is, that the liquid contained within the pock--the lymph--escapes only partly through a puncture made in the wall of the vesicle. In order to evacuate the pock thoroughly it is necessary to make a great number of punctures or a circular incision following the ring-like ridge of the bourrelet.

The lymph contained within the cells of the pock is a liquid which in its gross physical properties differs but little from the lymph which exudes from any traumatic surface shortly after the injury has been inflicted, as in the glazing process that takes place in wounds. Examined microscopically, however, it is found to contain not only the fibrin, the salts, the corpuscular elements, and the débris that ordinary tissue-juice presents, but also certain minute spherical bodies--termed microspheres, microzymes, vaccinads, etc.--that give it its characteristic infective quality and justify the title of virus commonly applied to it. That these minute bodies really constitute the virulent element of the lymph, or at least that they are the vehicle of the contagium, is not a mere matter of conjecture, but has been demonstrated abundantly, notably by Chauveau and Sanderson's diffusion experiments. Inoculation with the supernatant liquid, containing none of these bodies, always fails to convey the disease, but it is not absolutely essential that they should be present in large proportion in the lymph to render the latter virulent, for Chauveau found that lymph diluted with thirty times its bulk of water was not without infective {464} power. It scarcely need be said, however, that the greater the proportion in which they are present, the greater is the probability that the lymph will prove infective on inoculation. These bodies have been supposed to be of a vegetable nature, and Hallier, Kohn, and others have bestowed no little study upon their botanical characteristics. Under favorable circumstances they retain their virulent properties for a long time, especially if kept perfectly dry and not subjected to a high temperature. The present writer has met with success in the use of vaccinal virus seven years old.

The lymph differs somewhat in its gross appearances according as it is produced in man or in the bovine animal. In the former it is clear and limpid, and exudes freely in great drops when the pock is punctured in its peripheral portion; in the latter it is more straw-colored and more viscid, exuding sluggishly, or even refusing to flow without the aid of pressure. Moreover, the vaccinads seem endowed with different properties in the two cases: in man they have a tendency to remain equably diffused through the liquid, while in the cow they tend to separate from it and to be deposited upon any solid surface at hand.

The phenomenon termed umbilication, common to the vaccinal pock and to that of variola, has given rise to some differences of opinion as to the mechanism of its production. The term implies a depression at the centre of the pock. This appearance is not invariable, but it is constant enough to have met with general acceptance as a characteristic feature, notwithstanding the undoubted fact that it is found in lesions that have nothing whatever to do with any of the varioliform diseases. Not to waste space in discussing the various theories that have found supporters, it may be said that they have all been proved to be defective, save only the simple explanation that as the process of evolution advances the centre of the pock undergoes desiccation, whereby that portion of the tissue involved is so glued and drawn together as to become incapable of the swelling that is still going on in the growing peripheral portion of the lesion.

The crust into which the pock ultimately becomes converted is not, as is commonly supposed, mere dried lymph and nothing else; it is dried tissue enclosing concrete lymph. It generally includes also various sorts of débris--broken-down epithelium, blood-corpuscles, pus-corpuscles, and even, in rare cases, a core of sphacelated tissue like that of a furuncle.

As has already been said, the cicatrix is to a certain extent peculiar in that it is usually depressed and foveolated. Too much stress has been laid upon these features, however, and the truth is that some traumatic scars cannot be distinguished readily from that of vaccinia, while, on the other hand, many a genuine pock leaves no permanent trace behind it. Indeed, in the cow it is the exception for a noteworthy scar to form.

SEQUELÆ AND COMPLICATIONS.--The most important sequela of vaccinia is the fact that it protects the subject against small-pox, and on that circumstance hinges the chief practical interest of the disease. This leads us at once to the subject of vaccination, and therefore under that head we shall pursue our consideration of this curious affection.

{465} Vaccination.

SYNONYMS.--"The new inoculation;" Fr. Vaccination; Ger. Kuhpockenimpfung, Schutzpockenimpfung; It. Vaccinazione; Sp. Vacunacion.

HISTORY.--Before giving the history of vaccination itself (meaning by that term the intentional inoculation of vaccinia for the purpose of protecting the subject against small-pox), it may be well to devote a few words to a practice that preceded it--that of the intentional inoculation of small-pox (or simply inoculation, latterly called variolation). In very early times various Oriental peoples became aware of the fact that small-pox might be very decidedly mitigated by inoculation. This was practised in various ways, all of which may be reduced to the process of inserting small-pox virus into a solution of continuity. Lady Montagu, the wife of an English ambassador to Turkey, brought the practice back to England with her, where it soon made its way into popular favor, and whence it spread rapidly over Europe and America. Thus contracted, small-pox was shorn of a great part of its terrors; the eruption was usually trifling in amount, and in every way the disease was mild as a rule. Still, the mortality was something worth considering, and, worse than that, the inoculated disease was communicable by effluvium, so that an inoculated person had to be secluded carefully for fear of spreading the disease in the ordinary way. In all cases, too, careful medical treatment was thought necessary. On the whole, then, while inoculation was undoubtedly a boon, it was fraught with many grave perils. So great, indeed, were these perils, and so thoroughly were they appreciated, that the practice was interdicted by law in most civilized countries so soon as vaccination had become established in popular favor.

In several European countries the common people--at least those of them who had much to do with dairies--gradually became aware of the existence of the disease termed cow-pox, and of the fact that those individuals who had accidentally contracted it were rendered proof against the infection of small-pox. There is even fair testimony to show that some of these people, particularly the English farmer, Benjamin Jesty, relying on their observation to this effect, employed intentional cow-pox inoculation as a protective measure. These facts, however, do not detract in the least from the credit that all Christendom has awarded to a man who subjected the popular impression in question to the test of scientific investigation, proved its truth, and demonstrated its value to the world. That man was Edward Jenner, an English country physician. It was in the last quarter of the eighteenth century that he entered upon his course of inquiry, and on the eve of the present century he published his demonstration to the world. It was not a discovery; it was not an invention: it was more than either, "a matchless piece of induction," to quote the words of Mr. John Simon. Filled as he must have been with the consciousness of his great achievement, Jenner set this good example to all investigators: that he did not make haste to convert the world; he first convinced himself. It may almost be said, indeed, that, like Minerva from the head of Jove, the rational and perfected practice of vaccination sprang complete from Jenner's hands. Doubt and ridicule he had to encounter at first, and afterward envy and detraction; but the force of {466} his facts and the symmetry of his deductions were such that the new inoculation soon spread through the broad world, and has ever since maintained its sway, save with a few fanatical scoffers.

That vaccination really does protect against small-pox observation has taught the whole civilized world, if we leave out of account the few conscientious and intelligent doubters (made such, doubtless, quite as much by the extravagant statements often put forth by those who from time to time think it incumbent on them to defend vaccination, as by their own misinterpretation of facts) who are to be found associated with the noisy little body of actual opponents of the practice. One of the most injurious statements ever made in the advocacy of vaccination is, that it always protects if properly done. When one of these illogical defenders of that proposition is confronted with an instance that disproves his assertion, he falls back on the allegation that in that instance the vaccination was not properly done. The manifest absurdity of such an argument strikes the doubter most forcibly, and inclines him to say to himself, Falsus in uno, falsus in omne. Unbelief founded on this ground would never have arisen if the plain truth had always been adhered to: that the protection afforded by vaccination is not invariable, and that very often it is not permanent. In the infancy of the practice these facts were not known, but it is now many years since they became obvious to every fair-minded observer. The misapprehension of facts lies chiefly in the false deduction from the circumstance that the great majority of cases of small-pox occur in persons who have been vaccinated. But the explanation of this is very simple. Suppose that, of one hundred persons vaccinated, twenty fail to be protected permanently; that all persons not vaccinated are unprotected; and that throughout the civilized world the proportion of vaccinated to unvaccinated persons is as ninety to ten. Making no pretence of arithmetical accuracy, it may certainly be said that all these suppositions are well within the truth. It follows from them that in a community of ten thousand persons there will be nine thousand who have been vaccinated, and one thousand who have not. Of the former, eighteen hundred will have failed to secure lasting protection. Therefore in case of an epidemic there will probably be a proportion of eighteen cases of small-pox in the vaccinated to ten in the unvaccinated; and yet this should not obscure the fact that of the nine thousand vaccinated more than seven thousand were absolutely protected, whereas of the one thousand not vaccinated not one could escape the disease if exposed to it. When we add the further observation that of the eighteen hundred cases of small-pox among the vaccinated not more than thirty or forty would probably prove fatal, while of the one thousand cases in the unvaccinated about two hundred would end in death, we have a striking demonstration of the efficiency of vaccination. As a matter of fact, statistics show that the figures here given err rather in allowing too little than in asserting too much in favor of vaccinal protection.

The question naturally arises, Why it is that vaccination protects some persons and does not protect others?--reference being had, of course, to permanent protection, for it is exceedingly rare for temporary immunity to be attained if we exclude those instances in which the variolous infection has taken place before the operation is resorted to. This {467} question cannot be answered with any certainty, but various theories have been brought forward, some of which call for notice.

In the first place, it has been thought that the revolution of the system termed puberty was fraught with such a radical change as to do away with the mild modification due to vaccination. While this theory has an air of plausibility, it seems to lack proof and not to be upheld by analogy, for we do not find that children who have had scarlet fever, measles, and the like often undergo those diseases a second time on arriving at the age of puberty.

The only remaining theory that our limits will allow a consideration of is that put forward by Marson of London, that the degree and duration of vaccinal protection are proportionate to the perfection of the vaccinal lesion and to the number of insertions made. In a large experience with small-pox Marson found that the disease was more fatal among those whose vaccinal scars were imperfect or few in number than among those who bore evidence that several pocks had been produced and had run a typical course. As to the influence of a perfect evolution of the lesion, but little doubt can be entertained, for we have already seen that in some instances its course is so different from what it should be that no protection whatever seems to result. When we come to consider the number of the pocks as affecting the degree or the duration of protection, however, an obvious source of fallacy arises in the fact that we cannot always be sure that some of the scars on a person having a number of them were not the products of a repetition of the operation several years after the first--that is to say, a revaccination, the efficiency of which in restoring lost immunity is now well established. Nevertheless, as long as the doubt remains the best course to pursue seems to be to act as if Marson's theory were in all respects correct, and vaccinate by multiple insertions.

We have, then, no positive means of ascertaining who those persons are that are likely to fail of lasting protection, or how long a time will elapse before the cessation of their immunity will take place. The only safety lies in revaccination. But after how many years should revaccination be resorted to? It has been thought that this question might be settled by noting at what age, or at what period after primary vaccination, large numbers of people became susceptible of revaccination. This test, however, is not altogether trustworthy, for a renewed susceptibility to vaccinia by inoculation does not necessarily imply that the liability to take small-pox by effluvium has been regained. If it did, modified small-pox (varioloid) would be far more common than it is, for it is certain that revaccination can be made to succeed in a very large proportion of children long before they have reached the age of puberty. The fact is, contrary to the notions of the last generation, that success in revaccination is the rule, not the exception. Formerly it was not expected to succeed, and therefore no special pains were taken to ensure success.

Definite rules cannot be laid down as to the time that should be suffered to elapse before vaccination is repeated, but in the great majority of instances safety may be attained by revaccination every five or six years, and always in the presence of an epidemic, regardless of the lapse of time; also whenever one's mode of life is to undergo a noteworthy change, {468} as in emigrating to a foreign country, on entering the military service, and the like.