the cause, or avoiding it in some way or other so that the body may remain unaffected, (a) The antiseptic method introduced by Lister is a good instance of the methods which aim at destroying the cause before it has acted, (b) Residence in high localities, drainage, etc., are instances of the methods by which the causes of disease may be so attenuated or diluted as to become harmless, (c) Absolute cleanliness. Aseptic methods are based on the possibility of avoiding certain causes entirely without destroying them.
2. Protection consists in so modifying the possible host as to render it able to resist virulent parasites. This can be done either by (a) increasing its strength and activity, as by diet, warmth, functional activity, (and other hygienic conditions (Wargunin); (b) rendering its tissues and fluids unsuitable media for the growth or full development of the parasite—inoculation and Jenner's vaccination are good instances of that method, which has been further extended by Pasteur and others; (c) by establishing tolerance (Sewall, 1887).
3. The curative methods consist in attenuating or entirely destroying the virus causing the disease after it has penetrated into the body. (a) The actual destruction of the parasite within its host is apparently still a desideratum, (b) Attenuation of the virulence can be obtained by introducing into the blood and tissues some product either interfering with the full development of the parasite or modifying the tissues and fluids of the body so as to increase their resistance to the extension of the parasite or to its products. This seems to be the chief principle at the root of Pasteur's vaccination for hydrophobia, etc. (c) Neutralizing the physiological action of the virus by using its physiological antagonist. Muscarine, for instance, may be antagonized by atrophine. Lauder Brunton (1873) directed attention to the possibility of applying this principle to the treatment of cholera. (The same idea has been applied to the treatment of poisoning by snake venom. Wynter Blyth, 1877; Lacerda, 1881.) (d) Destroying and removing the substratum or ground which has become contaminated by the parasite. This is apparently the view which Koch has taken of the action of his lymph. The action of the product on the tissues is, however, of the same kind as that of the substances used in some of the methods already mentioned, but more intense, and Koch's views will probably have to be modified.
In this attempt to analyze the methods which have been proposed I have separated processes, many of which may act concurrently. This is, however, of little consequence, for my object was less to give an account of any single method than to trace the development of the ideas which are at the basis of the treatment of
