Page:George Archdall Reid 1896 The present evolution of man.djvu/231

Rh symptoms, and practically in the same time. When inoculated from the dog to the monkey, however, the virus becomes less virulent; it is said to be attenuated or weakened, the attenuation becoming more and more marked in successive inoculations from monkey to monkey; the course of the disease becomes longer and longer, until eventually there may come a time at which the virus, when introduced under the skin or into the cranial cavity, is not sufficiently active to cause the death of this species. If this attenuated fluid be now inoculated into a rabbit, a dog, or a guinea-pig, it still remains comparatively weak for a time, through successive inoculations on these animals—i. e. at first it does not kill, then it kills, but only after a considerable time; but gradually the virulence returns, until at last it reaches its original level of malignancy, whilst if the successive inoculations are made in rabbits with primary fluid from either the dog or the monkey, the virulence may become so exalted that it is considerably greater even than that of the virus taken from the street dog, which at one time Avas supposed to be the most virulent form except that of hydrophobic wolves, which has always been known to be specially fatal; the virulence is doubled as the inoculation period is reduced to onehalf."—Woodhead, Bacteria and their Products, p. 320.

"Pasteur... subjected the bacilli" (of anthrax in a pure culture, i.e. in an artificial nutrient medium free from other kinds of micro-organisms) "'to a temperature of from 42° to 43° C.; these were found to have lost all their vitality at the end of about six weeks, this loss of vitality during the six weeks going on progressively in proportion to the rise of temperature. It is stated that at the outset the pure culture had all the virulence of anthrax blood; Whilst only half of the sheep inoculated with the culture that had been heated for ten days succumbed to anthrax. On the twenty-fourth day of heating, the culture, when inoculated, although givingrise to mild febrile disturbance, did not cause the death of a single animal. It was found, too, that if uoav, twelve days after the first inoculation, these surviving