578 BACTERIOLOGY. 



In like manner, the repeated injection of milk of one 

 species of animal into another will result in the forma- 

 tion of precipitins in the blood serum of the treated 

 animal that will precipitate the milk of that species of 

 animal from which the milk was derived. 



AGGLUTININS. In acquired immunity as the result 

 of recovery from a bacterial disease, and in induced 

 immunity after repeated injections of dead or living 

 cultures of bacteria, the blood serum acquires the prop- 

 erty of agglutinating the bacteria causing the infection. 

 This agglutination, as it is called, is brought about by 

 the presence in the blood serum of an antibody that has 

 the property of bringing about the clumping of the 

 bacteria and causes the cessation of motility in suspen- 

 sions of motile bacteria. This form of antibody is 

 spoken of as "agglutiuin." The specific action of the 

 agglutinin is of such a nature that it has for a long time 

 been employed as a means of diagnosing certain dis- 

 eases, especially typhoid fever, the reaction being known 

 under the name of Widal reaction. 



It has been found that normal blood serum of both 

 man and the domestic animals contains normally agglu- 

 tinins for a variety of bacteria (Bergey). 1 The normal 

 agglutinins are usually present in relatively low amounts, 

 though occasionally individuals are encountered that 

 possess this property to an unusual degree. These 

 " common " agglutinins, as they are called, may be 

 removed from the serum by saturation with related 

 organisms, but the specific agglutinins resulting from 

 immunization with a particular organism are not removed 

 in this manner. 



The agglutination reaction is frequently employed for 



1 Bergey : Journal of Medical Research, 1903, vol. v., p. 21. 



