Part 19

The clearest proof that the neutrophil, eosinophil, and mast cells are entirely separated from one another by the fundamental diversity of their protoplasm, of which the granulation is but a specially striking expression, is afforded by the study of the various forms of leucocytosis. As will be shewn in detail in the following chapter, neutrophil and eosinophil leucocytes behave quite differently in their susceptibility to chemiotactic stimulation. Substances strongly positively or negatively chemiotactic for one cell group are as a rule indifferent for the other; frequently indeed there is an exactly opposed relationship, inasmuch as substances which attract the one kind repel the other. Still greater is the difference between the mast cells and the other two cell groups; for so far as present investigations go, they are quite uninfluenced by substances chemiotactic for the neutrophil or eosinophil cells.

As specific cellular secretions, various kinds of granules must also be sharply marked off from each other by their chemical properties. The granules of the blood corpuscles seem to be of very simple chemical constitution. We have special grounds for the assumption that the crystalline granulations are for the most part composed of a single chemical compound, not necessarily highly complex even, but which seems to be a relatively simple body such as guanin, fat, melanin, etc. Doubtless other granulations have a more complicated constitution, and very often are a mixture of various chemical substances. The most complicated granules of the blood are the eosinophil, which are, as has elsewhere already been mentioned, of a more complex histological structure. For a peripheral layer is plainly distinguishable from the central part of the granule. It should be mentioned that according to Barker the eosinophil granulations appear to contain iron.

The key-stone of the hypothesis of the secretory nature of the granules is the direct observation of a secretory process in the cells bearing the granules. Naturally these researches offer extraordinary difficulties since only the coincidence of a number of lucky circumstances would allow the passage of dissolved granule substance into the neighbourhood to be followed. Kanthack and Hardy have succeeded in demonstrating the secretory nature of the eosinophil granules of the frog. When, for example, anthrax bacilli are introduced into the dorsal lymph sac of the frog they exert a positive chemiotaxis on the eosinophil cells. The latter come in contact with the bacilli, and remain for some time attached to them. During this period Kanthack and Hardy observed a discharge of granules from these cells, which now possess a protoplasm relatively homogeneous. Afterwards these cells move away from the bacilli, and are succeeded by the polynuclear neutrophil cells, as will be mentioned later. These authors were further able to observe gradual accumulation of granules in eosinophil cells in lymph kept under microscopic observation as a hanging drop, and thus demonstrated that they undergo the two stages characteristic of secretion, (1) appearance of granules within the cells, (2) discharge of these granules externally.

The mast cells too seem suited for this purpose since their specific substance is strongly characterised by its peculiar metachromatic staining, and is further especially readily recognisable, since by its great affinity for basic dyes it remains plainly stained, even in preparations that are almost quite decolorised. In fact appearances of the mast cells are not infrequently found, which must be referred to excretory processes of this kind.

In the first place it is occasionally seen that the mast cell granulation is dissolved within the cell, and diffuses in solution into the nucleus. In place of the well-known picture of the mast cell (see page 76) of a colourless nucleus, surrounded by a deeply stained metachromatic granulation, a nucleus is present intensely and homogeneously stained in the tint of the mast cell granulation, surrounded by a protoplasm shewing but traces of granules.

Still more convincing is the presence of a peculiar halo of the mast cells, described by various authors. Ehrlich first shortly mentioned this halo in his book on the oxygen requirements of the organism. A few years ago, Unna, whose notice Ehrlich's remark had no doubt escaped, described an analogous condition as follows: "in some nodules the mast cells appeared in part twice as large as usual, especially with the new mast cell stain (polychrome methylene blue, glycerine ether mixture). This was caused by the staining of a large round halo, in the centre of which lay the peculiar long-known mast cell, consisting of blue nucleus, and an areola of deep red granules. Higher magnification shewed that the halo was not granular, but very finely reticular; although it exhibited exactly the same red colour as the granules. It was consequently a spongioplasm peculiar to these mast cells."

The appearance of the mast cells described by Unna may also be artificially produced, by allowing a preparation that is stained with the oxygen containing analogue of thionin, oxamine, to remain for some time in lævulose syrup or watery glycerine. Evidently part of the dyed mast cell substance is dissolved and retained in the immediate neighbourhood. But as Unna possesses great experience of the mast cells and is a complete master of the methods of their demonstration, one must suppose that the halos described by him were preformed, and did not arise during the preparation of the specimen.

It must hence be concluded that an analogous process may go on during life, that these halos are the expression of a vital secretion of the substance of the mast cells externally.

A condition that Prus has brought forward in the so-called purpura of the horse, is also to be interpreted as a secretory process of the mast cells. He describes young mast cells from the hæmorrhagic foci of the wall of the gut, on the margins of which bodies of various sizes appeared, and which differ essentially from the mast cells themselves by their staining. Nevertheless from their whole configuration and position it is evident that these bodies have arisen in the mast cells themselves; and Prus comes to the conclusion "=that the degenerating young mast cells secrete a fluid or semi-fluid substance, which as a rule sets on the surface of the cells, but also, more rarely, in their interior=."

Evidence that the substance of the granules is given off externally may sometimes be seen in the polynuclear neutrophil or their analogues. Thus in rabbit's blood in which he had experimentally produced leucocytosis, Hankin found a distinct progressive decrease of the pseudoeosinophil granules on allowing the samples of blood to remain some time in the thermostat. Further in suppurating foci in man, especially when suppuration has lasted long, or the pus has remained for some time in the place in question (Janowski) a rarefaction almost to complete disappearance of the polynuclear neutrophil granules occurs, and is to be explained by a giving up of the granulations to the exterior.

These facts and considerations, on the whole, lead then to the conclusion, =that in general the granules of the wandering cells are destined for excretion. This elimination of the granules is probably one of the most important functions of the polynuclear leucocytes.=

FOOTNOTES:

Farbenanalytische Untersuchungen XII. zur Geschichte der Granula, p. 134.

loc. cit. pp. 5, 6.

Altmann's freezing process would be similar to the advance always insisted on by Ehrlich. It offers such great technical difficulties, however, that it has up to now been little used.

The cause of these misunderstandings is the tinctorially different stages of development of the granules, as we have fully explained above. How little adequate tinctorial differences by themselves are to settle the chemical identity of a granulation, is at once evident on consideration of the granules of other organs. No one surely would assert, that a liver, muscle, or brain cell could occasionally secrete trypsin, simply because the granules of the pancreas stain similarly and analogously to those of the cells mentioned. We would here expressly insist that we only assume a distinct character for each kind of granulation, in the strict sense of the term for the cells of the blood, since they possess a relatively simple function. In very complex glandular cells, however, with various simultaneous functions, several kinds of granules may be contained.

From a paper of Calleja we learn that Ramon y Cajal recognised the halos of the mast cells, and interpreted them in the manner we have above. Calleja also describes these halos and the method of demonstrating them in detail (thionin staining, and mounting the sections in glycerine). We must mention, however, that we do not consider this method suitable for the recognition of preformed halos, for the reasons above mentioned.

IV. LEUCOCYTOSIS.

The problem of leucocytosis is one of the most keenly debated questions of modern medicine. An exhaustive account of the various works devoted to it, of the methods and results, could fill by itself a whole volume, and would widely exceed the limits of an account of the histology of the blood. We can only deal fully therefore with the purely hæmatological side of the subject.

Virchow designated by the name "=Leucocytosis=," a transient increase in the number of the leucocytes in the blood; and taught that it occurred in many physiological and pathological conditions. In the period that followed particular attention was paid to the leucocytosis in infectious diseases, and to the investigators of the last 15 years in this province we owe very important conclusions as to the ~biological meaning~ of this symptom. Above all Metschnikoff has done pioneer service in this direction by his theory of phagocytes, and though his theory has been shaken in many essential points, yet it has exercised a stimulating and fruitful influence on the whole field of investigation.

To sketch Metschnikoff's doctrine in a few strokes is only possible by a paraphrase of the very pregnant words "Phagocytes, digestive cells." These words express the view, that the leucocytes defend the organism against bacteria by imprisoning them by the aid of their pseudopodia, taking them up into their substance, and so depriving them of the power of external influence. The issue of an infectious disease would chiefly depend on whether the number of leucocytes in the blood is sufficient for this purpose.

This engaging theory of Metschnikoff has undergone important limitations as the result of further investigation. Denys, Buchner, Martin Hahn, Goldscheider and Jacob, Löwy and Richter, and many others have demonstrated, that the most important weapon of the leucocytes is not the mechanical one of their pseudopodia, but their chemical products ("Alexine," Bucher). By the aid of bactericidal or antitoxic substances which they secrete, they neutralise the toxines produced by the bacteria, and thus render the foe harmless by destroying his weapon of offence, even if they do not exterminate him.

An explanation of the almost constant increase of the leucocytes of the blood in bacterial diseases is given by the chemiotactic as well as by the phagocytic theory of leucocytosis. The principle of =chemiotaxis= discovered by Pfeffer asserts that bacteria, or rather their metabolic products, are able to attract by chemical stimulus the cells stored up in the blood-forming organs ("positive chemiotaxis"). In the cases in which a diminution of the leucocytes in the blood is found, it is the result of a repulsion of the leucocytes by the bodies mentioned, =negative chemiotaxis=.

As the experimental investigation of leucocytosis was carried further, it was found that leucocytosis, quite similar to that occurring in infectious diseases, could also be brought about by the injection of various chemical substances (bacterio-proteins, albumoses, organic extracts and so forth); and it became evident that the explanation of the process by chemiotaxis must be supplemented in many respects. Löwit for instance found that when substances of this kind are injected, two different stages can be distinguished in the behaviour of the leucocytes. First came a stage in which they were diminished ("leukopenia," Löwit) and in such a way that only the polynuclear cells were concerned in the diminution, whilst the number of the lymphocytes was unchanged. After this came the phase of increase of the white blood corpuscles; and here too exclusively of the polynuclear cells; the =polynuclear leucocytosis=. This behaviour seemed to indicate that during the first period a destruction of white blood corpuscles brought about by the foreign substances took place, and that it was only the dissolved products of the latter which caused the emigration of fresh leucocytes by chemiotaxis. But new objections were raised against this view. Goldscheider and Jacob, in particular, shewed by exact experiments that the transient leukopenia of the blood was not true but merely apparent; and was caused by an altered distribution of the white blood corpuscles within the vascular system. For whilst in the peripheral vessels from which the blood for investigation was usually obtained, there was in fact a diminution of the leucocytes, "=hypoleucocytosis=," in the capillaries of the internal organs, especially of the lungs, a marked increase of the leucocytes, "=hyperleucocytosis=," was found.

There are other objections to the great importance that Löwit has given to leukopenia. À priori it is quite incomprehensible that the various substances, which in the fundamental test-tube experiment are able to exercise a distinct chemiotactic influence on the leucocytes, should under other circumstances need the intervention of the products of decomposition of the white blood corpuscles. Moreover clinical experience speaks in general against Löwit's theory. For in infectious diseases hyperleucocytosis is very common; and a transient leukopenia is equally rare.

This contradiction to the experimental results obtained by Löwit is easily explained when one reflects how different from the natural processes of disease are the circumstances of experiment. In this case the animal is by intravenous injection flooded at once with the morbid substance, and a violent acute reaction of the vascular and blood systems is the natural consequence. In natural infection, insidious and increasing amounts of poison come quite gradually into play, and for this reason, perhaps, hypoleucocytosis in the normal course of infectious diseases is much rarer than in the brusque conditions of experiment.

Upon the clinical importance of leucocytosis, particularly for the infectious diseases and their various stages, an enormous mass of observations has accumulated. Selecting pneumonia as the best studied example, in the typical course of this disease the constant occurrence of leucocytosis is undisputed; the increase usually continues up to the crisis, and then gives place to a diminution of the leucocytes until a subnormal number is reached.

Of special importance are the observations on an absence of leucocytosis in particularly severe or lethally ending cases (Kikodse, Sadler, v. Jaksch, Tschistowitch, Türk and others).