244 MILK 



order of antibodies in Ehrlich's theory of immunity. Antibodies 

 of the third order require the presence of two substances before 

 they can react, namely, the amboceptor, which is the true im- 

 mune body, and the complement, which is a substance present in 

 normal blood. When either of these substances is lacking the 

 presence of the other cannot be detected. The failure to find 

 bactericidal substances in milk may be due, therefore, to the 

 absence of complement, although amboceptor may be present. 

 When milk is taken by the young mammal the amboceptor, if 

 present, may pass into the circulation, where it is activated by 

 the complement of the blood. It is possible then that antibodies 

 of Ehrlich's third order are present in milk, but escape detection 

 in absence of the complement. But the amboceptor passes into 

 the blood of the young and its presence can then be demonstrated, 

 since complement is normally present in blood. 



Some investigators have found hemolysins and bactericidal 

 substances in milk, while others have failed to find them. Since 

 complement is frequently absent in normal milk or present in 

 small quantity, it seems probable that the amboceptor is com- 

 mpnly present, but remains inactivated because of lack of com- 

 plement. 



In abnormal milk derived from diseased animals complement 

 is more abundant than in normal milk, and bactericidal substances 

 and hemolysins are readily detected. 



Applying the principles of immune body formation, several 

 interesting biologic tests have been devised by means of which 

 adulteration of the milk of one mammal with milk from another 

 can be detected. Bauer claimed that he was able to find cow's 

 milk in human milk in the proportion of 1 : 1000. By similar 

 tests mastitis milk or colostrum milk, if mixed with normal milk, 

 can be detected. However, these methods have not been prac- 

 tised to a great extent, and it is unwise at this time to consider 

 them entirely satisfactory. As a rule, biologic tests take much 

 time and expensive material, and, furthermore, they require such 

 skill and experience that competent operators are necessary to 

 conduct them. On the other hand, their usefulness cannot be 

 questioned, since early discovery of pathologic conditions of an 

 animal makes it possible to eliminate it from the herd before 

 clinical symptoms are sufficiently obvious. It is highly probable 

 that with more experience and research biologic tests will develop 

 which may become highly useful. Descriptions of certain biologic 

 tests are here given : 



The Precipitin Test. A rabbit is injected intraperitoneally or 

 intravenously with a few cubic centimeters of a certain milk sus- 

 pected of having been used as an adulterant. The injection is 



