282 STUDIES IN IMMUNITY. 



I. PROPERTIES OF ANTISENSITZERS. 



The antisensitizer should be chosen with some care in order to 

 render its study most fruitful. The antisensitizing power is fre- 

 quently only slightly developed in antisera and is often detectable 

 only by delicate methods; in which cases very large doses of anti- 

 serum must be used to neutralize the sensitizer effectively, and such 

 doses are often inconvenient for various reasons. 



For this reason one must use an antiserum with marked antisen- 

 sitizing properties and also an active sensitizer. It is necessary, 

 too, that the normal sera of the animals furnishing the sensiti- 

 zer and the antisensitizer respectively should be as inactive as pos- 

 sible, as they are used as controls to contrast with the peculiar 

 properties of the immune sera. These conditions are very satis- 

 factorily realized in the following example: 



The sensitizer we have" generally used is the serum of rabbits 

 that have been given three or four injections of from 5 to 7 c.c. 

 each of defibrinated bovine blood. In certain other experiments 

 we have used as well the serum of rabbits immunized against other 

 blood corpuscles, for example, human and hen corpuscles. The 

 antisensitizer employed is the serum of guinea-pigs that have 

 received two or three injections of 3 to 5 c.c. each, at intervals of 

 from 12 to 15 days, of normal rabbit serum. These animals are bled 

 2 weeks after the last injection. 



Before being used for experiments, both sera are deprived of 

 alexin by heating for a half hour to 55 to 56 C. As we already 

 know, this temperature has no effect on the sensitizer or antisensi- 

 tizer. For simplicity, we refer to our sensitizers as " rabbit > ox, 

 56 degrees/' " rabbit > hen, 56 degrees," " rabbit > human, 56 

 degrees, " and the antisensitizer as guinea-pig > rabbit antiserum, 

 56 degrees. The control sera are normal rabbit serum, 56 degrees, 

 normal guinea-pig serum, 56 degrees. 



What is the best method of demonstrating antisensitizing power? 

 Two widely divergent methods may be considered. 



First, sensitizer and antiserum may be mixed, the corpuscles 

 used as a reagent subsequently added, and a determination made 

 as to whether they have become sensitized by subsequently adding 

 alexin. This method is one frequently employed. It makes use 



