182 STUDIES IN IMMUNITY. 



Normal rabbit serum is the one in which agglutinins best resist 

 heating, so far as we have studied them. Rabbit serum must be 

 heated to approximately 65 degrees to cause any distinct diminu- 

 tion in agglutinating power either for corpuscles or bacteria. 



When we come to compare the effect of heat on the normal and 

 on the specific agglutinins we find very distinct correspondence. 

 In such experiments it should be remembered that specific agglu- 

 tinins are very much more energetic and, consequently, any dimin- 

 ution in their activity is less evident than in normal sera, the 

 energy of which is slight to begin with. In experiments on the 

 sera of the goat, rabbit, or guinea-pig vaccinated against the cholera 

 vibrio, and the serum of the dog vaccinated against B.' typhosus, 

 the specific agglutinating property is distinctly diminished by any 

 temperature that weakens a normal agglutinating power; in the 

 case of the guinea-pig and the goat this diminution is evident after 

 heating to 61 to 62 degrees; and the sera heated to 70 degrees are 

 almost inactive. The agglutinins in immune rabbit serum are 

 much more resistant; and, as we have just seen, the same fact holds 

 true for the normal agglutinins in normal rabbit serum. Two 

 cholera sera coming from a rabbit and a guinea-pig respectively 

 resist heat differently; on heating them to 70 degrees there is marked 

 diminution of activity in the specific guinea-pig serum, but only a 

 very faint diminution in the specific rabbit serum. It may be 

 noted that rabbit serum also resists coagulation by heat better than 

 does guinea-pig serum. Guinea-pig serum mixed with equal parts 

 of normal salt solution becomes opalescent, but is not coagulated, 

 on heating to 65 degrees for a half hour; rabbit serum treated in 

 the same way does not even become opalescent; it becomes faintly 

 opalescent only on heating to 70 degrees. We need scarcely em- 

 phasize the fact that there is apparently some close relation between 

 the appearance of a coagulation or opalescence and the deteriora- 

 tion of active substances. 



In short, it may be said that agglutinins, whether affecting cor- 

 puscles or bacteria, are similarly affected by heat whether they occur 

 in normal sera or in specific sera. There is a progressive diminution 

 in activity as the temperature is raised, but it is impossible to define 

 a critical temperature below which they remain intact and above 

 which they are destroyed. Agglutinins appear to be more resistant 



