30 COLLECTED STUDIES IN IMMUNITY. 



different. This was positively proven by the fact that the anti- 

 isolysin A was entirely ineffectual against isolysin B. The difference 

 between these two isolysins is further illustrated by the difference 

 of the intervals between blood injection and isolysin formation. In 

 the one case this was only a few days and in the other fourteen days. 

 That the injection of the goat blood should result in the formation 

 of two entirely distinct and easily differentiated icolysins was cer- 

 tainly a remarkable phenomenon. And yet this did not exhaust 

 the multiplicity of the isolysins. 



In a third goat, C, (injected on the same day as B and with sim- 

 ilar amounts of the same blood,) a haemolysin C appeared on the 

 seventh day which again differed from isolysins A and B. This, 

 furthermore, proved itself an isolysin, for the blood-cells of the ani- 

 mal were entirely insensitive to its action, though they were sensitive 

 to isolysins A and B. This fact shows that isolysin C differed from 

 isolysins A and B. It is specially noteworthy that, although the two 

 goats B and C were injected at the same time with similar amounts 

 of the same blood, they should develop different isolysins. This 

 observation is particularly important because it shows that the 

 constitution of the isolysin is dependent on the individuality of the 

 animal in which it is developed. 



It is also very remarkable that these three isolysins, A, B, and C, 

 were able to destroy not only goat blood-cells, but also those of 

 sheep. The sheep erythrocytes therefore possess three different 

 groups which are identical with those of these goat blood-cells, or 

 at least are closely related to them. On the other hand still another 

 isolysin, D, does not dissolve sheep blood-cells. 



After having observed three different isolysins in three different 

 goats, we are in no wise to assume that this exhausts the possibilities. 1 

 On the contrary, it seems highly probable that by further experi- 

 ments we shall come to know other isolysins. Nevertheless it must 

 not be assumed that this variation of the isolysins is unlimited. 

 It is to be expected that a sufficient repetition of the experiments 

 will finally lead us to recognize a certain cycle of constantly repeat- 

 ing types. The attainment of this goal, however, is rendered very 



1 Note on revision. In the mean time we have obtained a fourth isolysin, 

 D, which differs from isolysins B and C in the fact that it dissolves the blood- 

 cells of B and C. Erythrocytes of A are not dissolved, but the isolysin differs 

 from A in its behavior to various normal kinds of goat blood. The behavior 

 of isolysin D toward sheep blood has already been mentioned. 



