626 THE POPULAR SCIENCE MONTHLY. 



With these facts in view, let us proceed to consider briefly the 

 various theories which have been offered in explanation of ac- 

 quired immunity : 



Exhaustion Theory. For a time Pasteur supported the view 

 that during an attack of an infectious disease the pathogenic 

 micro-organism, in its multiplication in the body of a susceptible 

 animal, exhausts the suyjply of some substance necessary for its 

 development, that this substance is not subsequently reproduced, 

 and that consequently the same pathogenic germ can not again 

 multiply in the body of the protected animal. 



In discussing this theory, in a paper published in the Ameri- 

 can Journal of the Medical Sciences (April, 1881), the writer 

 says: 



Let us see where this hypothesis leads us. In the first place, we must have a 

 material of small-pox, and a material of measles, and a material of scarlet fever, 

 etc. Then we must admit that each of these different materials has been formed 

 in the system and stored up for these emergencies attacks of the diseases in 

 question for we can scarcely conceive that they were all packed away in the 

 germ-cell of the mother and the sperm-cell of the father of each susceptible 

 individual. If, then, these peculiar materials have been formed and stored up 

 during the development of the individual, how are we to account for the fact 

 that no new production takes place after an attack of any one of the diseases in 

 question ? 



Again, how shall we account for the fact that the amount of material which 

 would nourish the small-pox germ, to the extent of producing a case of confluent 

 small-pox, may be exhausted by the action of the attenuated virus (germ) intro- 

 duced by vaccination ? Pasteur's comparison of a fowl protected by inocula- 

 tion with the microbe of fowl cholera, with a culture fluid in which the growth 

 of a particular organism has exhausted the pabulum necessary for the devel- 

 opment of additional organisms of the same kind, does not seem to me to be a 

 just one, as in the latter case we have a limited supply of nutriment, while in 

 the former we have new supplies constantly provided of the material food 

 from which the whole body, including the hypothetical substance essential 

 to the development of the disease-germ, was built up prior to the attack. Be- 

 sides this, we have a constant provision for the elimination of effete and useless 

 products. 



This hypothesis, then, requires the formation in the human body, and the re- 

 tention up to a certain time, of a variety of materials which, so far as we can 

 see, serve no purpose except to nourish the germs of various specific diseases, 

 and which, having served this purpose, are not again formed in the same system, 

 subjected to similar external conditions, and supplied with the same kind of nu- 

 triment. 



It is unnecessary to discuss this hypothesis any further, inas- 

 much as it is no longer sustained by Pasteur or his pupils, and is 

 evidently untenable. 



The Pretention Theory, proposed by Chauveau (1880), is sub- 

 ject to similar objections. According to this view, certain prod- 

 ucts formed during the development of a pathogenic micro-or- 



