268 RECEPTORS OF THE THIRD ORDER 



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 Vvith 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 "cyto- 

 toxic" means "cell poisoning" or "injuring," while "cyto- 

 lytic" means "cell dissolving." The latter term is the one 

 generally 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 

 hacteriolysin, a hemolysin (red-corpuscle-lysin) , epitheliolysiri 

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

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

 as "bacteriocidin," "spermo toxin," "neurotoxin," etc. 



The use of the term "cytolysin" is also not strictly correct, 

 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 noiinal serum (which contains only a very 

 little cytolytic substance, so that it has no dissolving power 

 when so diluted) the mixture again becomes cytolytic. 

 It is evident then that in cytol^^sis there are two distinct 

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

 or immune, and the other present in large quantity only in the 

 immune cytolytic serum. This may be more apparent if the 

 facts are arranged in the following form : 



I. Immune serum dissolves cells in high dilution. 

 II. Heated immune serum does not dissolve cells. 



III. Normal serum in high dilution does not dissolve cells. 

 II. +111., i. e.. Heated immune serum plus diluted normal 

 serum dissolves cells. 



