extended for extreme pain; oedema of the eyelids and legs, difficulty of moving the tongue, profuse clammy perspirations, inflammation of the lungs, exhaustion, unconsciousness, and death. After death numberless living trichinæ were found in all the striated muscles, including those of the heart, some straight and some coiled, in all different stages of development. The parasite is bisexual, producing its young alive in the mucus of the intestines, in which it lives and moves freely; from thence the immature forms bore their way into the muscles, wherein they become encapsuled for a longer or shorter time, but may resume their activity and go through their complete stages and propagate again in the intestines. The whole process may be gone through in three to four weeks. The discovery of this horrible parasitic disease produced a profound sensation in all civilised countries, and it became evident that it could be nothing new, but an explanation was merely given of various anomalous epidemic and solitary cases of disease hitherto set down as typhoid or unknown forms of fever. It afforded, also, a good example of the ultimate tendency of the reduction of disease to parasitic exciting causes, viz., that for the protection of society against such diseases we must rely on police regulations for destruction of the sources, rather than on medicine, for in this case the latter was powerless to find a remedy. And in all such cases where the whole tissues or the blood are pervaded by innumerable microscopic organisms, it is hardly to be expected that we shall find substances which shall be poisons to these low creatures and at the same time harmless to the infinitely higher organisation of the host.

Another parasitic disease may be noticed derived from the vegetable kingdom, viz., the "fungous-foot " or " madurafoot" of India.

In this disease the spores of a mucedinous fungus penetrate the skin of the naked feet of the natives through small

accidental cracks or abrasions. These being capable, like true parasites, of living in the healthy fluids and tissues, grow rapidly and, with the tremendous molecular force of growing organisms, bore their way even into the bones, causing destruction of them and of the soft parts, with suppuration and wasting fever, so that death is only averted by amputation of the limb. Specimens of this fungus sent home to Mr. Berkeley were cultivated by him, and identified with the genus Chionyphe, and named by him, after the discoverer of the disease, Chionyphe Carteri. We have here, therefore, an example of a true parasitic disease, and one of peculiar interest, as it has been supposed to throw light on the nature of hospital gangrene, which is the scourge of military hospitals. Another disease traced to a parasite, this time animal, is the endemic dysentery of Egypt, which has been found to depend on the presence of a fluke-like worm, called the Bilharzii hæmatobium. Finally, we may note the more recent discovery of Dr. Lewis, of Calcutta, that the disease of the kidney, called Chyluria, and certain forms of Elephantiasis (a kind of leprosy), depend upon the presence of the Filaria sanguinis, a parasite which inhabits the blood-vessels. And here we may notice the still more recent discovery of Dr. Manson, of China, as throwing light on the mode of communication of infectious diseases, viz., that these worms are actually conveyed to men or animals by mosquitoes, which suck up the small worm with the blood of their victims, and thus transfer them to other living creatures.*

§ 7. The above are certainly proofs of the dependence of certain diseases, hitherto ranked among the miasmatic and contagious, on the presence of parasitic animal and vegetable organisms. So far, therefore, such a class of diseases exists.

*

It is possible that we have here an explanation of the destructive power of the Tsetse fly, for it may be the intermediate host of some similar blood-parasite; or it may be the carrier of some infective poison. It is highly improbable that any mere poison or venom should exist so powerful as to cause the death of a large animal in such small dose.

But in all these cases the parasites are tolerably large and well-defined morphologically specific organisms; and the diseases themselves are comparatively rare, and differ so considerably from the common specific and infectious diseases, that it is only by somewhat straining the definition that they can be brought within the class. Are there examples among the true specific forms, such as measles, scarlet-fever, typhus, smallpox, &c., in which the universal presence of a special parasitic organism can be shown? The answer can now be given prima facie in the affirmative in respect to two human diseases, viz., the splenic fever or anthrax, or malignant pustule of cattle and men; and the relapsing fever of

men.

The anthrax, or malignant pustule, is a disease of extreme virulence and fatality both in cattle and in men, and is extremely contagious, so that a drop of the blood of an infected animal falling upon any uncovered part of the skin, even if unbroken, will produce the characteristic boil, followed by speedy infection of the whole blood. The course of the disease is extremely rapid, proving fatal in a few hours in some cases, and in most within a day or two; the symptoms being general disturbance, shivers, followed by febrile heat, debility, muscular twitches; then convulsions, hæmorrhages, and total collapse, with coldness and inability to move, difficult breathing, and death. In this fearful disease bacterial organisms were discovered in the blood by Davaine, about twenty-five years ago, and they were seen at different intervals since. Still their presence for long was not looked upon as an essential feature in the disease, and even in 1866 no mention is made of them in Aitkin's text-book of Medicine. Within the last eight or ten years, however, proofs have been gradually accumulating of the causal connection of this bacterium with the disease, and the observations of Dr. Koch, in 1876, are generally considered to amount to

positive demonstration.

The facts are, that the blood is always found to contain an abundance of rod-bacteria, supposed by Davaine originally to constitute a distinct species, and, therefore, named Bacteridia, but which are pronounced by F. Cohn not to be distinguished morphologically from the Bacillus subtilis of the butyric fermentation, and, therefore, called by him Bacillus anthracis. The mode of action of the contagium is peculiar; the actual contact of the blood or exudations of a diseased animal infects another with certainty, but "animals placed in the closest proximity to the diseased ones, and placed in the most favourable circumstances for infection through the air, are not infected." (B. Sanderson.) The infective power of the blood is transitory, and is lost on the appearance of ordinary putrefaction, and it cannot be kept for more than a week generally, or at most five weeks, without losing its activity. Nevertheless, it is a fact that the contagion can exist in a persistent form, and lurk about stables and sheds for months, and even years, and can be transported across the Atlantic in hair and wool, thus infecting by air-borne dust. The blood, while capable of infecting, always contains the above bacilli, but when filtered through porcelain is no longer poisonous. The explanation of these facts is given by the experiments of Dr. Koch, since confirmed by those of Dr. Ewart, of University College, London.* It was found that the bacilli, at the height of the disease, are still growing and immature, and if such blood is quickly dried in small portions, or undergoes ordinary putrefaction, the bacilli perish, and with them the power of infection. But if a drop of the fresh blood, with living

* Lecture on the Germ Theory, by Dr. Burden Sanderson, 1878. Dr. Ewart has since published his results in the Quarterly Microscopical Journal, April, 1878. He finds that the rods are not motionless, as stated by Davaine. The formation of spores requires a moist state and a temperature between 28 and 33 C; and that it took place as well after death and out of the body. A heat of 37 C prevents the germination of the bacilli.

bacilli, is placed in serum at the temperature of the body, the bacilli soon begin to grow enormously in length, become studded with bright oval dots, and finally break up, leaving those dots, which are in reality spores, possessed of immense powers of resistance, and capable of germination after drying and passing through numberless vicissitudes. The same formation of spores may take place in larger masses of spleen or blood slowly dried. Thus are explained the fugitive and the persistent forms of the contagium-the one depending on the living bacillus, and the other on the spores. The reason why the infective power of the living blood is speedily lost is that the bacilli are propagated therein solely by fissiparous generation; and it is only in the blood of the dead animal, or in suitable dead nutriment, that the formation of spores takes place. Koch then proved by observation that these spores reproduce the rod-bacilli. Next, by experiment, he showed that these bacilli from cultivated spores had the same pathogenic activity as the fresh bacilli from the living animal; for by inoculation with the spores death was produced by splenic fever, with its usual abundance of the bacilli. He also noticed that in a specimen which most of the spores had fallen to the bottom, while few remained floating in the liquid, inoculation with the bottom fluid, thus richer in spores, produced death within twenty-four hours, while that with the surface fluid only in three or four days. The inoculation with the cultivated spores is no doubt the crucial test, for inoculation with blood containing bacilli does not prove that the contagium resides in the bacilli; it might reside in some other poisonous matter introduced at the same time; whereas the cultivated spores may be presumed to be free from other non-parasitic contagious poison. I am bound, however, to say that, on careful perusal of the details of the experiments, it appears to me the possibility of that was not excluded. To show that the cause of death in these inoculations was not