196 MANUAL OF BACTERIOLOGY. 



Morgenroth and Sachs* found great variation in cytolytic 

 power in serum of various sorts. Thus the serum fiom a horse 

 at one drawing was hemolytic for rabbits' corpuscles but not 

 for those of guinea-pigs; three days later the serum from the 

 same horse was strongly hemolytic for guinea-pigs' corpuscles, 

 but only very slightly for rabbits' corpuscles; twenty-three days 

 later the serum from this horse was not hemolytic for guinea- 

 pigs' corpuscles, but strongly hemolytic for rabbits' corpuscles. 



It is therefore evident that the cytolytic power of serum is 

 very variable. Not only does the blood from different indi- 

 viduals of the same species differ in this respect, but the serum 

 from the same individual differs from time to time. This is 

 probably the case with all animals. 



The peculiar behavior of immune sera on dilution will be 

 described under immunity. 



Precipitins. Precipitins are bodies which develop in the 

 serum of animals which have been given subcutaneous injec- 

 tions of albuminous substances, and which, added to solutions 

 of the albumin with which the animals have been injected, 

 cause these to become cloudy and finally form a precipitate. 

 Thus a rabbit's blood-serum may be sensitized by injections 

 of hen's egg-albumen, and the rabbit's blood-serum will then 

 precipitate hen's egg-albumen. It may, however, imperfectly 

 precipitate albumen from the egg of a species closely allied 

 to the hen. 



Again, a rabbit injected a few times at intervals of a day 

 or two with human blood-serum furnishes serum which even 

 in small quantities causes precipitation even in a weak solution 

 of human blood-serum, such as may be obtained from old 

 dried blood-spots. 



The effect produced by the injection of foreign albumin 



* Alfred Petterson. Ueber die natiirliche milzbrandimmunitatdeshundesund 

 des huhns. Cent. }. bakt., abt. i, Orig., bd. 33, no. 8, p. 613-626. Jena, 

 Apr. 4, 1903. 



