148 IMMUNOLOGY 



Natural and Immune Bacterial Agglutinins. — The capacity of 

 normal or immune sernm to bring about the specific clumping 

 (^■glutination) of bacteria depends upon its antibody content. 

 The titer of normal agglutinins varies from zero to one in ten or 

 one in twenty ; rarely is it found higher. On the other hand the 

 titer of agglutinin following vaccination or recovery from in- 

 fection is usually quite high in comparison. This subject will be 

 discussed in a later chapter. 



Hemolysins, Hemagglutinins and Other Antibodies. — While 

 l>ordet was busily engaged in explaining the mechanisms of l)ac- 

 teriolysis by immune serum, an important observation of Buchnei- 

 nttraeted his attention. The latter had observed that occasionally 

 normal blood serum had the property of destroying and hemo- 

 lyzing foreign red blood cells in vitro (outside the body). Bordet 

 wondered whether this phenomenon was dependent upon a sensi- 

 tizer or amboceptor and complement mechanism such as he had 

 shown for bacteriolysis and whether he could make specific 

 sensitizer or amboceptor appear in the blood stream of animals 

 by vaccinating them with a suspension of foreign red blood cells. 



By a series of simple experiments he showed that in a normal 

 rabbit whose blood serum had little if any effect upon sheep red 

 cells, he could, by injecting it several times with washed sheep 

 cells, cause the appearance in the blood stream of the rabbit, within 

 about a week after the last injection, of an appreciable amount of 

 sensitizer or hemolysin for sheep cells. He found that this new 

 sensitizer or hemolytic amboceptor for red cells was thermolabile, 

 that it did not possess the property of destroying the cells, but, like 

 bacteriolytic sensitizer, it rendered the red cells susceptible or 

 sensitive to the digestive or lytic action of complement. This re- 

 sulted in the liberation of hemoglobin from the red cells, a 

 phenomenon which is called hemolysis. 



The natural antibodies causing hemolysis and agglutination of 

 foreign red cells are called heterohemolysins and heteroJiemagglu- 

 tinins, respectively, while similar antibodies that result from 

 vaccinating with foreign red cells are called immune liemolifsins 

 and immune hemagglutinins, respectively. 



Landsteiner observed early in this century that human blood 

 could be arranged into several groups, depending upon the prop- 

 erty of human blood serum from one person clumping and fre- 



