160 INFECTION AND IMMUNITY. 



test-tube experiments by mixing the blood cells of 

 one animal with the serum of another which is 

 toxic (e. g., rabbit blood + g a t serum). This is 

 the phenomenon of hemolysis, and the appearance 

 of such a tube is exactly like that seen when blood 

 is mixed with distilled water or even with tap 

 water ; i. e., it is a laking of the blood, it loses its 

 opacity and assumes a beautiful cherry-red color. 

 The serum of practically every species contains a 

 hemolytic substance (a serum hemolysin) for 

 some kind of erythrocyte. 



cytotoxins. Some serums also contain toxic agents for other 

 cells; they are generally called serum cytotoxins. 

 The serum of the eel not only contains a strong 

 hemolysin, or hemotoxin, but also a powerful 

 poison for nervous tissue, neuro toxin. Similarly 

 we have normal leucotoxins for leucocytes, nephro- 

 toxins for kidney tissue, etc. 



Another property of many normal serums is 

 that which causes agglutination or clumping of 

 bacteria, as one sees it in the Gruber-Widal test 

 for typhoid. Even normal human serum may ag- 

 glutinate the typhoid bacillus, but to a less degree 

 than that of a typhoid patient. 

 i. One serum often causes a precipitate in the 

 serum of another animal, or in a bacterial culture 

 filtrate. 



In many instances, a foreign serum which is 

 not particularly toxic on first injection, becomes 

 very poisonous when administered (subcutane- 

 ously) a second time. (See "Anaphylaxis.") 



In considering these facts, one becomes con- 

 scious of the great complexity of that substance 

 which plays so important a part in immunity and 

 its study i. e., the blood serum. 



