Part 104

The study of yellow-fever poison after the objective method has hitherto been unproductive of definite results. When such experienced and truthful observers as Sternberg, Woodward, and Schmidt, working with the most approved microscopes, have failed to identify any organism or object peculiar to the products from the bodies of yellow-fever subjects or to the circumfusa of the sick, this declaration is sufficiently supported.

{641} But when we turn to a subjective method of investigating that toxic agent which causes yellow fever, it is found to possess sufficiently well-marked characteristics to justify practically valuable conclusions. Some of these characteristics or modes of behavior merit notice.

1st. The human system is a field of reproduction and multiplication of yellow-fever poison. This is sufficiently established by two facts:

(a) A person in the incubative stage of yellow-fever intoxication may be divested of all fomites and yet originate other cases after a developed attack.

(b) The infection is intensified by aggregation of the sick.

These propositions are indisputably true.

2d. The poison or infection undergoes some change after leaving the human system. This appears to be susceptible of proof, because communication of the disease from person to person is not a common event. When this does apparently occur, there is often very strong reason for a belief that the contagion was resident in some fomites connected with the patient's bed or clothing.

3d. There are no sustained observations which prove that yellow-fever poison is ever created de novo.

The autochthonous birthplace of the poison is unknown. The suggestion of Niebuhr, that yellow fever may have been one of the causes of death during the plagues of Athens, can not be authoritatively denied. It may have been called into existence at the moment when all things else were created which were to perpetuate each its kind.

4th. Some of those conditions and circumstances which favor or retard the development or maturation of yellow-fever poison outside the human body are quite well understood. Warm, damp weather is most prominent among those climatic conditions which are favorable to the growth of yellow-fever epidemics.

5th. A freezing temperature ordinarily destroys the contagium of yellow fever. A high degree of artificial heat produces a similar result. It is highly probable that certain chemical agents would also effect its destruction if brought in contact with it.

6th. If yellow-fever fomites are hermetically enclosed in situations protected from cold or other agents which are destructive to their infection, its vitality may be preserved for an undetermined length of time, and its toxic qualities again made manifest when unacclimated persons are exposed to it.

7th. Yellow-fever poison possesses ponderability. This characteristic is so distinctly marked that it has been frequently termed a "low-lying poison."

8th. It is incapable of being air-borne through any great distance, at least without being deprived of its toxic effects.

9th. It is transportable in fomites through great distances, either on sea or land, and as often as its toxic effects are manifested after these portations they are so uniform as to be promptly recognizable.

A great number of different materials in common use may act as fomites, such as loose wool, cotton, or hair, or textile fabrics of various descriptions.

The following facts, which illustrate how yellow-fever infection may be conveyed in the most unsuspecting and innocent manner, are well {642} authenticated. There can be no ground for accusation of error except in the hypothesis that the infection was encountered simultaneously in some unexplained manner. The facts are furnished by Dr. Shannon of Ocean Springs, Mississippi: "On the 14th of October, 1883, Maj. J. B. B. died of yellow fever in Ocean Springs, Miss. I moved the family at once to the healthy locality where you saw Miss B., not allowing them to take any article from the room where the husband and father had died. The children applied to me for a lock of their father's hair, which I refused, but the oldest daughter, now dead, prevailed upon the nurse to give it her. She placed it in an old envelope that had been torn open at the end and carefully folded the torn end down, thus practically sealing it, and laid it away among other old letters. On Sunday, the 4th of November, at 12.30 P.M., she brought this envelope out upon the open gallery, and opened it for the first time to examine the lock of hair and show it to her aunt, Miss S., who was visiting her, and upon inhaling the concentrated poison confined in the envelope and emanating from the hair, exclaimed, 'Oh, what a peculiar smell!' She then handed the envelope to her aunt, Miss S., who, unconscious of danger, also inhaled the 'messenger of death' with a similar exclamation, when Mrs. B., who was standing near, reached out her hand for the envelope, but was prevented from getting it by the entreaties of a fretful child to be taken up in her arms. This gave time for sufficient reflection, and she admonished the young ladies of the possible danger. The envelope was then carefully folded, and with its fatal contents replaced in the drawer where it had been since the 14th of October. This drawer had been almost daily opened. On the following Saturday night, Nov. 10th, at 9 P.M., Miss S. was taken sick with a chill, and Miss B. at about 2 A.M., some five hours later, the period of incubation being less than seven days in both cases. No other person handled the fatal envelope or in any way came in contact with it, and there is, after the most careful inquiry, no suspicion of any other source of infection in these two cases. Miss S. died on Oct. 14th, Miss B. on Oct. 16th."

10th. These qualities of yellow-fever infection, and especially its faculty of reproduction (which only organisms possess), furnish almost conclusive evidence that yellow fever is a germ disease produced by a specific contagium vivum.

Many facts are patent which sustain the generally accepted opinion that yellow-fever poison gains admission to the system through the medium of atmospheric air. On the other hand, I know of no observations which prove that the disease is ever communicated by food or drinks, or through any other vehicle than atmospheric air.

In respect to atmospheric infection by yellow fever, localizations of aërial impregnation are often observable, not common in other air-infecting diseases. A certain district of a large and populous city may become the seat of a sweeping and fatal epidemic, and yet no case occur outside of this area of prevalence. It is customary to speak of these points of epidemic prevalence as infected localities. If unprotected persons visit such infected places, even for a short period of time, they are liable to attacks of yellow fever, although they may take neither food nor drink within the limits of infection and bring no fomites away with them. Under these circumstances atmospheric impregnation is conclusive.

{643} But it is difficult to determine how this infection of a locality has been produced in the first place, and how, in the second place, it is maintained sometimes for periods of from one to three months, with so little apparent diminution or change in the liability to communicate yellow fever to unprotected visitors within the limits of infection.

It seems highly probable that yellow-fever poison, after its exit from the human body, attaches itself to various solid surfaces in proximity to the sick, where, under suitable climatic conditions, it undergoes more or less speedy processes of maturation in toxic qualities. The poison thus matured is capable of being preserved with but little change for the periods indicated above, and is communicable through the atmosphere for short distances. It is also capable, by virtue of some unexplained process or quality, of spontaneously extending its area of infection. But this is at all times slow, and is readily interrupted by streams of water, high walls, or even by much-travelled thoroughfares.

There are no instances in which the water-supply of cities has been shown to have distributed yellow fever.

The periods of time which may intervene between exposure to yellow-fever poison and attacks of the disease are extremely variable. The shortest period of incubation which has come under my observation was about twenty hours. In three cases in which I was able to fix the hours of first exposure with precision attacks followed in 72 hours, 83 hours, and 101 hours, respectively. Of 55 unacclimated physicians who exposed themselves at Memphis during the epidemic of 1878, 54 suffered attacks of yellow fever. In these cases the periods of incubation varied from one to twenty-five days, the average duration being ten days. These physicians all remained steadfastly at their posts of duty; consequently, the attack which occurred on the twenty-fifth day was postponed for that length of time during constant exposure in a locality most intensely infected.

It must be true that many cases of individual resistance to the effects of yellow-fever infection depend upon states of the system or idiosyncrasies which diminish liability to the action of the poison. In other words, their personal receptivity to it is lessened by certain constitutional states.

That this position is correctly taken is proved by the fact that many circumstances which violently disturb the system determine attacks in persons who may have for a long time enjoyed immunity from them. Anxiety, grief, fright, fatigue, or exposure to sudden wettings or cold may precipitate attacks, either by disturbing vital processes by which the system is ridding itself of the poison--so far, at least, as to prevent an accumulation great enough to occasion attacks--or by lowering powers of resistance through enfeeblement of nerve-force.

But it can be affirmed in regard to yellow-fever poison that it is not more capricious or eccentric in its behavior as an infection than that of scarlet fever. Each of these diseases may appear in a large family of unprotected persons with a degree of violence which results in death in every instance, and suddenly cease, leaving a greater or less number of the household without attacks, though equally exposed with those who have died.

One attack of yellow fever confers immunity from the disease during after life. A person who has suffered an attack is said to be acclimated {644} or protected. Neither of these terms should be applied to those who have not suffered attacks, however long they may have withstood exposure during epidemics. It often occurs that persons who have escaped attacks through many years of renewed exposure at last succumb to the disease. On the other hand, I know of three well-authenticated instances of immunity in a sweeping epidemic of persons whose mothers had suffered attacks during the gestations which respectively resulted in their births.