In the last century typhus was distinguished definitely and clearly from "typhoid" or "enteric" fever, and from "relapsing" or "famine" fever, with which it had previously been confounded. The bacterial germs causing enteric and relapsing fevers are now known, and have been isolated and cultivated, and the mode in which they are conveyed into the body of a previously healthy patient is ascertained. But until the past year we knew neither the parasitic germ which causes typhus fever nor the mode by which it passes from one individual to another. A vague idea that it was spread through the air prevailed. Typhus is remarkable for the frequency with which the nurses and doctors attending a case become infected. About 20 per cent. of those attacked by it die, but in persons above forty-five years of age the mortality is much greater—about half succumb.
Dr. Nicole and his colleagues of the Institut Pasteur in Tunis have recently had the opportunity of studying typhus there. They found that the ordinary local monkey could not be made to take the disease. But a drop of blood of a typhus patient injected into a chimpanzee (which is far nearer akin to man) produced the disease after an incubation period of three weeks. This fact was definitely established. From what is now known as to relapsing fever, malaria, yellow fever, plague, and sleeping-sickness, it seemed probable that some migratory insect must be the carrier of the typhus infection from man to man. The typhus patients brought into the hospital at Tunis were carefully washed before admission, and no infection of other patients or nurses took place in the wards, although the cases were not isolated, and bugs were abundant. The only cases of infection which occurred were in persons who had the duty of collecting and disinfecting the clothing of the patients when admitted. This seems to exclude the bug as a carrier. The flea is excluded by the fact that in the phosphate mines of Tunis the flea is abundant, and bites both natives and Europeans. Yet when typhus fever broke out among the miners—although all were equally bitten by the fleas—no European was infected. The indication, therefore, was that if any insect is the carrier, it is neither the flea nor the bug, but probably the clothes-louse. Although the smaller monkeys cannot be directly infected with typhus fever from man, it was found that (as with some other infections) the bonnet monkey was susceptible to the infection after it had passed through the chimpanzee. Experiments were, therefore, made with clothes lice taken from a healthy man, and kept for eight hours without food. They were placed on a bonnet monkey which was in full typhus eruption. A day afterwards they were removed to healthy bonnet monkeys with the result that the healthy bonnet monkeys developed typhus fever. There is thus no doubt whatever that typhus fever can be carried in this way from bonnet monkey to bonnet monkey. The whole history of typhus fever fits in with the carriage of the infection in the same way from man to man, and not with the notion of an aërial dispersion of the infection.
The fact that typhus only exists in very dirty and crowded populations, and that it has disappeared where even a moderate amount of cleanliness as to person and clothing has become general, coincides with the possibility of the body louse as carrier. This little parasite is known to be a wanderer, and is gifted with a very acute sense of smell. An individual placed in the centre of a glass table invariably walked, guided by the scent, towards the observer, at whatever position he placed himself. Sulphurous acid is a violent repellant of these creatures. Not only will it kill them if they are exposed to its fumes, but traces of it drive them away. Hence doctors and nurses who have to handle typhus patients or their clothes have only to wear a small muslin bag of sulphur under their garments, or to rub themselves with a little sulphur ointment in order to be perfectly guarded against infection; the louse will not approach them, nor remain upon them should it accidentally effect a lodgment.
It is not always obvious at once in what way a knowledge of the mode of carriage of a deadly disease can be of service to humanity. But in this case it is strikingly and triumphantly clear. In the vast poverty-stricken population of Russia typhus is still common. Public medical officials attend these cases, and the Russian Government keeps a record of the annual deaths of its medical staff, and of the causes of their deaths. In the first six months of last year 530 Russian medical officers died, and twenty-four of these deaths were caused by typhus fever acquired by these devoted public servants in attendance upon cases of that fever. Henceforth they will make use of sulphur or sulphurous ointment to keep the little infection-carriers at a distance, and not one medical man or nurse will catch the disease, still less be killed by it.
A remarkable fact in this history is that the actual parasitic germ which causes typhus, whether a bacterium (Schizophyte) or a protozoon, has not been detected, although the louse has been shown to be its "carrier." The same is true of yellow-fever: we have not seen with the microscope the microbe which produces it. But we know with certainty that the gnat, Stegomya fasciata, and no other, is the carrier of the unseen germ, and that we can obliterate that fever by obliterating the gnat. So, too, although we know how the infection of rabies acts, and how it is carried, yet no one has yet isolated and recognised the terrible infective particle itself. There is a very high probability that in these cases, and also in cancer (where as yet no specific infective germ or parasitic microbe has been detected), such an infective microbe is nevertheless present, and has hitherto escaped observation with the microscope on account of its excessive minuteness and transparency.
CHAPTER XXI
CARRIERS OF DISEASE
It has now been discovered that a great number of human diseases are caused by microscopic parasites, which are spoken of in a general way by the name invented by the great Pasteur, viz. "microbes." Wool-sorter's disease, Eastern relapsing fever, lock-jaw, glanders, leprosy, phthisis, diphtheria, cholera, Oriental plague, typhoid fever, Malta fever, septic poisoning and gangrene have been shown to be caused each by a peculiar species of the excessively minute parasitic vegetables known as bacteria (or Schizophyta). Others, for example, malaria and sleeping sickness, have been shown to be caused by almost equally minute microbes, which are of an animal nature, and similar to the free-living animalcules which we call Protozoa, or "simplest animals," whilst a third lot of diseases—rabies, smallpox, yellow fever, scarlet fever, and typhus—are held to be caused by similar minute parasites, although these have not yet actually been seen and cultivated, but are surely inferred (from the nature and spread of these diseases) to exist.