68 RELATION OF BACTERIA TO DISEASE ' 



are formed, again called anti-, or in general, antibodies. 

 Three will be considered: (1) The antibodies 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. Eacteriolysins . The first antibodies cause a dissolving 

 of the bacterial cells. These antibodies are called bacterio- 

 lysins (adj., bacterioly tic) . There is in all blood, whether 

 normal or subjected to immunizing 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 fever, 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 phagocytes, 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 

 numbers of germs incapable of producing disease are intro- 

 duced, the power of these cells may be stimulated for the 

 particular kind of germ introduced and not for others. The 

 bodies producing this increased eating or phagocytosis, 

 opsonins, are supposed not to act upon the cells, but upon the 

 bacteria and make them more suitable as food for the phago- 

 cytes. These phenomena have put a valuable method of 

 treatment in the physician's hands. In subacute localized 

 disorders particularly, but also in definitely acute and 

 chronic troubles, injections of dead cultures of the bacteria 

 responsible for the condition, are made beneath the skin. 

 The progress of treatment is followed by a long elaborate 



