IN MEDICINE. 21 



special form of germ which gives rise to many forms of disease. 



More recently, Pasteur has been carrying out a series of 

 experiments on the cholera of fowls, a disease virulent in the 

 highest degree, but which has the characteristic common to many 

 epidemic diseases, that one attack has the power of more or less 

 protecting the sufferer from subsequent infection. He has dis- 

 covered that the poison in this disease is a microscopic parasite, 

 which can be cultivated outside the animal by being introduced 

 into a suitable decoction , and also that, by making successive 

 cultures at prolonged intervals, he can reduce the virulence of the 

 virus, so that ultimately a poison is produced which will give the 

 disease in a mild form, but which, as vaccination is a protection 

 against small-pox, renders the fowl insusceptible to the severe form 

 of the disease. 



It has also been shown that another disease — Anthrax or 

 Splenic fever, a disease to which animals are subject, and which is 

 specially interesting from the fact that it gives rise to a serious and 

 fatal disease in man known as " wool-sorter's " disease — is pro- 

 duced in animals which have fed upon fodder containing germs of 

 a Bacteria — Bacillus antJwacis — and Dr. Greenfield has proved 

 that these germs also become progressively less virulent in 

 successive generations of artificial cultivation ; and he has thus 

 obtained a modified virus, producing more or less severe symp- 

 toms, and appearing to be partially protective against future severe 

 attacks. These experiments seem to open out the possibiHty of 

 reducing the virulence of the disease-germs of scarlatina, measles, 

 etc., so that a mild form can be given which will act as a 

 protection against the severer forms. Should this prove to be 

 practicable, the youth of the future will not only have to suffer 

 vaccination for small-pox, but will also have to undergo a mild 

 course of scarlatina, measles, typhus, typhoid, cholera, diphtheria, 

 whooping-cough, and all other germ-caused diseases. Under 

 these circumstances, I think it may be questionable how far the 

 earlier years of the life of future generations will be worth 

 living. 



In addition to these minute vegetable-parasites, we are also 

 at times called upon to play the part of host to various kinds of 

 animal-parasites, all of which take up their abode in some parts of 



