1886.] NEW YORK ACADEMY OF SCIENCES. :205 



This may possibly have been noticed where the diseases are of 

 the same character, differing only in intensity; but between 

 ■diseases of different characters it has not, I think, been made a 

 subject of investigation from statistics. There is nothing in any 

 of the theories to be advanced which would theoretically mili- 

 tate against such being the case, while in some inoculation ex- 

 periments, animals previously treated, but not with the virus at 

 that time being studied, have seemingly been less susceptible 

 than perfectly fresh subjects. 



Here, then, is a subject which may repay a little tabulation by 

 those having access to the required records. 



Three main theories have been advanced to explain immunity, 

 which can be named most conveniently by their distinguishing 

 •characteristics, as: 



1st. The "exhaustion" theory, followed by Pasteur. 



2d. The "antidote*'' theory, of which a discussion, avowedly 

 in its favor, can be found in Klein's recent " Micro-organisms 

 and Disease;" and 



3d. What 1 wish to call the "tolerance" theory, first put 

 forward, I believe, by Sternberg. 



Let us consider each in its turn. 



The "' exhaustion " theory is the first which would by its 

 simplicity be apt to be thought of. Its analogies with the con- 

 ceptions previously guiding the germ theory are most close. To 

 Pasteur, working for many years on Fermentation, it would 

 naturally occur; it is this: The blood and tissues of an animal 

 contain certain substances necessary to the life and multiplica- 

 tion of the disease germs; such substances are removed by the 

 germs either of mitigated virus or of the disease itself, and thus 

 -the aninuil is protected against subsequent attacks, since the sup- 

 ply of this particular aliment is wanting, and without it the 

 germ cannot thrive. The apparent analogy to alcoholic fer- 

 mentation is very striking. There we know the presence of a 

 particular substance (sugar) is necessary to the life and multi- 

 plication of the germ (yeast plant); that this substance serves 

 as food to the germ, is thus removed, and after removal the 

 liquor cannot again undergo fermentation of the same kind, 

 since the supply of aliment is wanting. We have seen how the 

 germ theory has gone hand in hand with fermentation, and it is 

 to the greatest worl^er in ferments that we owe this theory. But 

 is it tenable ? We do not think it is. 



We will quote Pasteur's own words in its defence, and then 

 ■discuss his statements. He says: "The explanation to which 

 these facts lead us, as well of the constitutional resistance of 

 some animals, as also of the immunity which protective inocula- 

 •tion gives rise to in fowls, is nothing else but natural when we 



