74 THE RELATION OF BACTERIA TO DISEASE 



In the case of the reaction of bacterial cells or their 

 endotoxins the result is more complicated. Many 

 substances are formed, again called anti-, or in general, 

 antibodies. Three will be considered: (1) The anti- 

 bodies which dissolve bacterial cells; (2) those which 

 clump them; and (3) those which encourage the white 

 cells of the blood to eat them. The substances exist 

 in minute quantities in normal blood. 



1. Bacteriolysins. The first antibodies cause a 

 dissolving of the bacterial cells. These antibodies 

 are called bacteriolysins (adj., bacteriolytic). There 

 is in all blood, whether normal or subjected to im- 

 munizing procedures, a substance called complement, 

 which makes possible these combinations of antibody 

 and germ. 



2. Agglutinins. Agglutinins are substances which 

 cause clumping of bacterial cells, but do not dissolve 

 them. They are made use of in the diagnosis of some 

 acute fevers, notably in the Widal reaction of typhoid 

 (see Typhoid Fever). 



3. Opsonins. These are substances which act upon 

 bacteria and prepare them for consumption by certain 

 cells of the body, especially of the blood, called phago- 

 cytes, a term applied because they have the power of 

 devouring foreign substances. Bacteria are such, and 

 it is the task of these phagocytes to remove them. 

 These cells are also migrating cells, as they leave the 

 blood stream and wander over the body. It has been 

 found that in some conditions their power of consuming 

 bacteria is below par, and, further, that if small num- 

 bers of germs incapable of producing disease are intro- 

 duced, the power of these cells may be stimulated for 



