114 THE SPECIFIC PRECIPITINS. 



Kraus, and subsequent investigations by others have shown that this 

 specific reaction holds good with all bacteria to which animals have 

 been immunized. 



The substance in the serum which enters into this reaction is 

 known as the precipitin and the precipitate thus formed is designated 

 as a precipitum. 



Bordet found that when milk which had been partially sterilized 

 by being heated for one hour at 65° was injected intraperitoneally 

 and this injection repeated at short intervals for some time, the 

 blood serum of the animals thus treated gives with the milk which 

 has been injected a precipitate. He' placed three c.c. of the serum 

 from the animal treated with the milk in one test-tube and the sera 

 of other animals in corresponding tubes as controls, and found that 

 on the addition of the milk which had been used in the treatment 

 of the animal, a precipitate appears, while no cloudiness occurs 

 on the addition of the same milk to other sera. On the ad- 

 dition of ten or twelve drops of milk to the homologous serum, 

 floccules form and slowly subside, leaving a clear supernatant 

 fluid, while in the other sera the milk diffuses, forming opalescent 

 homogeneous fluids. Further investigations, notably those of Was- 

 sermann and Schiitze,^ have shown that the serum of a rabbit treated 

 with cow's milk gives a precipitate with cow's milk and not with 

 the milk of any other animal, and that rabbits treated with goat's 

 milk furnish a serum that gives precipitates with goat's milk and 

 with no other milk ; and the same holds good when the experiments 

 are made with woman's milk. By this reaction the source of a given 

 sample of milk can be told with certainty. The following are the 

 details of an experiment of this kind : Several rabbits were treated 

 subcutaneously or intraperitoneally at intervals of from three to 

 four days with from 10 to 50 c.c. of cow's milk, sterihzed with 

 chloroform, while a like number were treated in the same way with 

 goat's milk, and a third lot treated with woman's milk. After the 

 rabbits had undergone this treatment for about three weeks and 

 each had received about 100 c.c. of milk, they were bled and their 

 sera, diluted 1 : 5, were added to milk, diluted 1 : 40, and these mix- 

 tures allowed to stand at room temperature for some hours. It was 

 found that the serum from the rabbits treated with cow's milk pre- 

 cipitated the albuminous substances in cow's milk, but had no such 

 action on the milk of either woman or goat ; while the serum of the 

 rabbit treated with goat's milk precipitated the casein of goat's milk 

 and had no effect upon that of the woman or the cow, etc. The 

 serum of animals that have been treated as above described with 

 milk is designated lactoserum, and it has been found that the 

 lactosera are in all cases specific in their reactions. Indeed, the dis- 

 covery of this reaction has shown that the proteids of the milk of 

 ' Deutsche med. Woehensckrift, 1900. 



