CYTOLYSINS 249 



puscles of another animal with which it had been injected. 

 Since this time the phenomenon has been observed with a 

 great variety of cells other than red blood corpuscles and 

 bacteria — leukocytes, spermatozoa, cells from liver, kidney, 

 brain, epithelia, etc., protozoa, and many vegetable cells. 



It is therefore a well-established fact that the proper 

 injection of an animal with almost any cell foreign to it 

 will lead to the blood of the animal injected acquiring the 

 power to injure or destroy cells of the same kind as those 

 introduced. The destroying power of the blood has been 

 variously called its "cytotoxic" or "cytolytic" power, though 

 the terms are not strictly synonymous since "cytotoxic" 

 means "cell poisoning" or "injuring," while "cytolytic" 

 means "cell dissolving." The latter term is the one gen- 

 erally used and there is said to be present in the blood a 

 specific "cytolysin." The term is a general one and a given 

 cytolysin is named from the cell which is dissolved, as a 

 bacteriolysin, a hemolysin (red-corpuscle-lysin), epitheliolysin, 

 nephrolysin (for kidney cells), etc. If the cell is killed but 

 not dissolved the suffix "cidin" or "toxin" is frequently used 

 as " bacteriocidin," "spermotoxin," "neurotoxin," etc. 



The use of the term " cytolysin" is also not strictly "cor- 

 rect, though convenient, for the process is more complex 

 than if one substance only were employed. As was stated 

 above, the immune serum loses its power to dissolve the cell 

 if it is heated to 55 ° to 56° for half an hour, it is inactivated. 

 But if there be added to the heated or inactivated serum a 

 small amount of normal serum (which contains only a very 

 little cytolytic substance, so that it has no dissolving power 

 when so diluted) then the mixture again becomes cytolytic. 

 It is evident then that in cytolysis there are two distinct 

 substances involved, one which is present in all serum, normal 

 or immune, and the other present only in the immune cytolytic 

 serum. Experiment has shown that it is the substance 

 present in all serum that is the true dissolving body, while 

 the immune substance serves merely to unite this body to the 

 cell to be destroyed, i. e., to the antigen. Since the immune 

 body has therefore two uniting groups, one for the dissolv- 

 ing substance and one for the cell to be dissolved, Ehrlich 



