KEGULATORS 615 



cytes, etc., by repeated injections of these substances into an 

 animal. Their action, is shown by their causing clumping or 

 agglutination when added to a suspension of the corresponding 

 antigen. Agglutinins may appear in the blood during an 

 attack of certain diseases, e.g. enteric fever, and the reaction 

 may be used for diagnosis. 



In these various cases, the active body is produced by the 

 throwing off of side-chains from the protoplasm, and, since these 

 products are carried away in the blood, the process is analogous 

 to the formation of internal secretions. 



Opsonins. — Many bacteria, after treatment with the serum 

 of the animal, are taken up by the leucocytes, but if not treated 

 with serum are not taken up. Apparently the serum contains 

 something, which has been called an oi:>sonin, which prepares 

 the bacteria to be devoured. The action of opsonins is destroyed 

 by temperatures between 55° and 65° C. The opsonic power 

 of the serum for a particular bacterium is often increased by 

 the injection of small quantities of that organism in the dead 

 condition (Vaccines). 



