IMMUNITY AGAINST BACTERIAL CELLS 143 



horse serum as from 0.004 to 0.000001 c.c. was found sufficient to 

 render a guinea-pig susceptible, and 0.1 c.c. was sufficient to kill a 

 guinea-pig that had been thus sensitized. Possibly this fact of devel- 

 opment of susceptibility may play an important part in the cases of 

 intoxication following administration of antitoxic serum. 1 



IMMUNITY AGAINST BACTERIAL CELLS 



By far the greater number of pathogenic bacteria do not 

 produce true soluble toxins, but form toxic materials which 

 accumulate within the cells, endotoxins ; these produce intoxica- 

 tion only when the bacterial cells are disorganized, liberating the 

 endotoxins. Against such endotoxins no antitoxic substances 

 have yet been produced by immunization. 2 The same is true of the 

 non-specific bacterial proteids. A certain degree of immunity 

 can be conferred to animals against the poisonous proteids iso- 

 lated from various bacteria in Vaughan's laboratory, 3 but it is 

 not comparable in any way to antitoxic immunity. Hence these 

 endocellular poisons are in some way different from the true 

 soluble toxins. 



If we immunize an animal against living bacteria, or against 

 the dead bodies of bacteria, or against endotoxins, and examine 

 the properties of its serum, we find that although the serum is 

 powerless to neutralize the poisonous effects of the bacterial 

 constituents, it does possess other marked properties, which are 

 quite the same no matter which of the materials mentioned was 

 used in immunization. The serum will kill bacteria both in 

 the test-tube and in the animal body ; that is, it is bactericidal. 

 It contains substances that cause the bacteria to agglutinate, 

 called agglutinins; and if motile, to lose their motility. It 

 contains substances that render the bacteria more readily ingested 

 by phagocytes ; these substances are called opsonins. And also 

 this serum will inhibit the action of the bacterial enzymes, and 

 will produce a precipitate in solution of the bacterial proteids, 

 i. e., it contains antienzymes and precipitins. All these proper- 

 ties are, to a certain extent, specific ; that is, they are exerted 

 chiefly or solely against the particular form of organism 

 that was used in immunizing. 4 Each property is also quite 



1 Full discussion by Rosenau and Anderson, Bull. No. 29, U. S. Gov't 

 Hygienic Lab., 1906; Jour. Med. Kesearch, 1906 (15), 179. Also see Wolff- 

 Eisner, Cent. f. Bakt., 1906 (40), 634; and Otto in v. Leuthold's Gedenkschr., 

 1906 (1), 1. 



2 Besredka (Ann. Inst. Pasteur, 1906 (20), 149) and a few others claim to 

 have secured antiendotoxins. 



3 American Med., 1905 (10), 145. 



* Welch (Med. News, 1902 (81), 721) has suggested that possibly the bac- 

 teria in their turn may develop antibodies for the tissues and fluids in which 

 they are growing. If so, we have a reasonable explanation of the development 



