meningitis may also accompany or follow the various diseases
that are set up by the Streptococcus pyogenes and Streptococcus
erysipclatis; whilst along with it staphylococci and the Bacillus
coli communis have sometimes been found. In other cases,
again, there is a mixed infection of the pneumococcus and the
Streptococcus pyogenes, especially in cases of disease of the
middle ear. As might be expected in meningitis occurring in
connexion with the specific infective diseases, e.g. influenza and
typhoid fever, the presence of the specific baciUi of these diseases
may usually be demonstrated in the meningeal pus or fluid.
4. The fourth form, tubercular meningitis (acute hydrocephalus), is met with most frequently in young children. It is now generally accepted that this condition is the result of the introduction of the tubercle bacillus into the blood-vessels and lymph spaces of the meninges at the base of the brain, and along the fissures of Sylvius.
Influenza. — From 1889 up to the present time, influenza has every year with unfaiUng regularity broken out in epidemic form in some part of the United Kingdom, and often has swept over the whole country. The fact that the period of incubation is short, and that the infective agent is extremely active at a very early stage of the disease, renders it one of the most rapidly spreading maladies with which we have to deal. The infective agent, first observed by Pfeiffer and Canon, is a minute bacillus or diplococcus less that i/i in length and o-5;u in thickness; it is found in little groups or in pairs. Each diplococcus is stained at the poles, a clear band remaining in the middle; in this respect it resembles the plague bacillus. It is found in the blood though here it seems to be comparatively inactive — and in enormous numbers in the bronchial mucus. It is not easily stained in a solution of carbol-fuchsin, but in some cases such numbers are present that a cover-glass preparation may show practically no other organisms. Agar, smeared with blood, and inoculated, gives an almost pure cultivation of very minute transparent colonies, similar to those of the Diplococcus pneumonia, but as a rule somewhat smaller. This organism, found only in cases of influenza, appears to have the power of forming toxins which continue to act for some time after recovery seems to have taken place; it appears to exert such a general devitalizing effect on the tissues that micro-organisms which ordinarily are held in check are allowed to run riot, with the result that catarrh, pneumonia and similar conditions are developed, especially when cold and other lowering conditions co-operate with the poison. This toxin produces special results in those organs which, through over-use, impaired nutrition or disease, are already only just able to carry on their work. Hence in cases of influenza the cause of death is usually associated with the failure of some organ that had already been working up to its full capacity, and in which the margin of reserve power had been reduced to a minimum. It is for this reason that rest, nutrition, warmth and tonics are such important and successful factors in the treatment of this condition.
Yellow Fever, endemic in the West Indies and the north-eastern coast of South America, may become epidemic wherever the temperature and humidity are high, especially along the seashore in the tropical Atlantic coast of North America. It appears to be one of the specific infective fevers in which the liver, kidney, and gastro-intestinal systems, and especially their blood-vessels, are affected. In 1897 Sanarelli reported, in the Annales de I'lnstitut Pasteur, that he had found a bacillus in the blood-vessels of the liver and kidneys, and in the ■'cells of the peritoneal fluid, but never in the alimentary tract, of yellow fever patients. These, he maintained, were perfectly distinct from the putrefactive microbes occurring in the tissues in the later stages, their colonies not growing like those of the bacillus coli communis. They grow readily on all the ordinary artificial nutrient media, as short rods with rounded ends, usually abtttit 2 to 4fi in length and about half as broad as they kre loh'^. ' They are stained by Gram's method and readily by mos't of the aniline dyes, are cihated, and do not liquefy gelatine. They flourish specially well alongside moulds, in the dark, in badly-ventilated, warm, moist places, and remain alive for some time in sea-water:
these facts, as Sanarelli points out, may afford an explanation of the special persistence of yellow fever in old, badly-ventilated ships, and in dark, dirty and insanitary sea-coast towns. Once the organism, whatever it may be, finds its way into the system, it soon makes its presence felt, and toxic symptoms are developed. The temperature rises; the pulse, at first rapid, gradually slows down; and after some time persistent vomiting of bile comes on. At the end of three or four days the temperature and pulse fall, and there is a period during which the patient appears comparatively well; this is followed in a few hours by icterus and scanty secretion of urine. There may be actual anuria, or the small quantity of urine passed may be loaded with casts and albumen; delirium, convulsions and hemorrhage's from all the mucous surfaces may now occur, or secondary infections of various kinds, boils, abscesses, suppuration's and septicaemia, may result. These often prove fatal when the patient appears to be almost convalescent from the original disease. As regards prognosis, it has been found that the " lower the initial temperature the milder will the case be " (Macpherson). An initial temperature of 106° F. is an exceedingly unfavourable sign. Patients addicted to the use of alcohol are, as a rule, much more severely affected than are others. Treatment is principally directed towards prevention and towards the alleviation of symptoms, though SanareUi has hopes that an " anti "-serum may be useful. More recently S. Flexner, working with the American Commission, isolated another organism, which, he maintains, is the pathogenetic agent in the production of yellow fever; whilst Durham and Myers maintain that a small bacillus previously observed by G. M. Sternberg and others is the true cause of this disease.
Professor Boyce, enumerating the hypotheses as to the cause of yellow fever, points out that as in the case of malaria, suspicion turned to " that form of Miasm which was supposed to arise from the mixture, in a marsh or on a mud flat, of salt with fresh water." It was early recognized that yellow fever was not carried directly from person to person, but little of definite character was known as to the poison and the method of its dissemination, and Fergusson states that " it is a terrestrial poison which high atmospheric heat generates amongst the newly arrived, and without that heat it cannot exist." The following passage from Beauperthuy (see his collected papers published in 1891) is quoted by Boyce: " But rubbish ! the small amount of sulphuretted hydrogen or marsh gas which might arise from a marsh could not possibly hurt a fly, much less a man. It is not that, it is a mosquito called in Cumana the ' Zancudo bobo, ' the striped or domestic mosquito." Beauperthuy, recently as he wrote, then stood almost alone in this opinion. Now we know that yellow fever, in common with other specific diseases, is caused by the action of an organized virus. The search for a vegetable parasite, bacillus or micro coccus, as above indicated, has been very close and strenuous, but it may now be held that up to the present no bacillus or micro coccus, well authenticated as capable of causing yellow fever, has been discovered. Latterly a search has been made for protozoa organisms, organisms similar to those present in the blood of malarious patients and like conditions, or for spirochaetes similar to those associated with relapsing fever, and Boyce draws attention to the fact that a spirochaete has recently been identified in the tissues taken from cases of yellow fever. It has however been demonstrated that the virus, whatever it may be, is carried by a species of mosquito; this seems to favour the protozoan hypothesis, especially as it is found that the Stegomyia fasciata, Fab. (or 5. calopus, Meig.), after taking the blood from an infected patient is not infective immediately but only becomes capable of infecting by its bite at the end of twelve days. It would appear therefore that residence in this mosquito is necessary for the material to become fully infective. During this period some special metamorphosis may occur, and metamorphosis essential to the development of the parasite, or, on the other hand, the time may be required for it to make its way to some position from which it may emerge from the mosquito when that insect
