174 



INFECTION AND IMMUNITY. 



Immune 

 Agglutinins. 



Immune Precip- 



itins and the 



Biologic Test 



for Species. 



By systematically injecting an animal with, a 

 bacterium or with any tissue cell, agglutinating 

 substances (agglutinins) are formed and may be 

 demonstrated in the serum. Like other antibodies, 

 they are highly specific for the cell used in the 

 immunization. 



It has been found that toxins, other than those 

 of bacterial origin, will yield 'antitoxins by im- 

 munization. Such toxins are snake venom, yield- 

 ing antivenin; ricin, a hemagglutinating toxin 

 from the castor-oil bean, yielding antiricin, etc. 



Kecently what is termed the biologic test for 

 species has assumed prominence. This test may 

 be illustrated : A goat is injected repeatedly with 

 the serum of man. After a number of injections 

 a very minute amount of this goat's serum will 

 cause a precipitate when mixed with human 

 serum, but not when mixed with the serum of any 

 other animal (except, perhaps, that of anthropoid 

 apes). The test is so delicate that when a small 

 amount of old dried human blood is dissolved in 

 salt solution and treated with the goat serum the 

 precipitation will still occur, and in view of this 

 fact, the test has become of medicolegal impor- 

 tance. 



The wide distribution of this phenomenon 

 among all kinds of animals gives it great biologic 

 significance, particularly as regards the differentia- 

 tion of species. 



Kraus found that by immunization with cer- 

 tain bacterial filtrates substances are formed in 

 the serum which cause precipitates in the filtrates. 

 It is further interesting that other albumin-con- 

 taining substances, as egg albumin or milk, will 

 on immunization, yield specific antibodies. The 



