192 PUBLIC HEALTH BACTERIOLOGY 



quantity of immune serum is added to a broth culture of 

 the respective bacterium, flake-like clumps sink to the 

 bottom of the tube, and the supernatant liquid becomes 

 clear. Grueber also showed that the immune serum 

 would affect in the same way, though less powerfully, 

 closely allied bacteria. The substances causing this are 

 called " Agglutinins," and were thought to be the same as 

 the " immune-body " concerned in Pfeiffer's reaction. 

 Both are comparatively thermostabile, but the agglutinins 

 cannot be reactivated by the subsequent addition of normal 

 serum. They do not act if NaCl is absent. 



Precipitation. In 1897, Kraus showed that precipi- 

 tates were formed when filtrates of cultures were mixed with 

 the corresponding immune serum. The " Precipitins," 

 like the agglutinins, are inactivated by heat (60 to 70 C.) 

 and cannot be reactivated (see SERUM PRECIPITATION, 

 below). 



Haemolysis. Bordet, in 1898, showed that the serum 

 of an animal which has been repeatedly injected with the 

 red corpuscles of another, acquires the power of dissolving 

 the red cells of that other, and that this power is lost on 

 heating to 55 C. but is regained by the addition of serum 

 of a non-treated animal. Other " cytotoxins " (cell- 

 destroying antibodies) similarly produced are : leucotoxin, 

 nephrotoxin, spermatotoxin, hepatotoxin, pancreatoxin, 

 suprarenal toxin, etc. 



Serum Precipitation. Like haemolysis, this subject 

 is closely allied to the reactions induced by bacteria. 

 When the serum of one animal is injected repeatedly into 

 another animal of a different species, a substance forms in 

 the first animal's serum, which causes, in a mixture of the 

 two sera, a cloudiness or precipitate to form. This 

 substance is called " precipitin," and is specific for each 

 species, in high dilutions, as in the case of the other 

 reactions. The precipitins, whether formed from bacterial 

 or serum stimulation (or casein of milk, etc.), are all 

 inactivated by heating to 60 to 70 C., but can not be 

 reactivated by the addition of normal serum or any known 

 method. Such inactivated serum, however, if mixed 

 with a certain amount of active serum, is able to prevent 



