IMMUNITY 471 



fourth day, they obtained a fluid which was highly toxic to guinea- 

 pigs (the fatal dose usually being 1 c.c. per 100 grrn. weight). The 

 symptoms closely resemble those obtained by Pfe'iffer. They found that 

 the toxicity of the filtrate was not altered by boiling — apparently this 

 toxic substance is different from Pfeiffer's endotoxin. Huntemuller has 

 obtained from various strains an acutely acting extracellular toxin which 

 is very labile and which he believes to be identical with the hemolysin. 

 He has obtained an antitoxin to this toxin. The diversity in the results 

 obtained by various workers seems only explicable on the view that 

 different strains vary greatly as regards production of extracellular toxin. 

 It may be stated that, as a rule, the, greater part of the toxic substance is 

 closely bound up with the bacterial protoplasm, and is only set free on 

 its disintegration. 



Immunity. — As this subject is discussed later, only a few 

 facts will be here stated, chiefly for the purpose of making clear 

 what follows with regard to the means of distinguishing the 

 cholera spirillum from other organisms. The guinea-pig or any 

 other animal may be easily immunised against the cholera 

 organism by repeated injections (conveniently made into the 

 peritoneum) of non-fatal doses of dead spirilla ; later the living 

 organisms may be used. In this way a high degree of immunity 

 against the organism is developed ; and further, the blood serum 

 of an animal thus immunised (anti-cholera serum) has markedly 

 protective power when injected, even in a small quantity, into a 

 guinea-pig along with five or ten times the fatal dose of the 

 living organism. Under these circumstance's the spirilla undergo 

 a granular transformation and, ultimately, solution ; this pheno- 

 menon is generally known as Pfeiffer's reaction, and was applied 

 by him to distinguish the cholera spirillum from organisms re- 

 sembling it. The following are the details : — ■ 



Pfeiffer's Reaction. — A loopful (2 mgrin.) of a recent agar culture of the 

 organism to be tested is added to 1 c.e. of ordinary bouillon containing 

 •001 c.c. of anti-cholera serum. The mixture is then injected into the 

 peritoneal cavity of a young guinea-pig (about 200 grm. in weight), and 

 the peiitoneal Huid of this animal (conveniently obtained by means of 

 capillary glass tubes inserted into the peritoneum) is examined micro- 

 scopically after a few minutes. If the spirilla injected have been cholera 

 spirilla, it will be found that they become motionless, swell up into 

 globules, and ultimately break down and disappear — positive result. If 

 they are found active and motile, then the possibility of their being 

 true cholera spirilla may be excluded — negative result. In the former 

 case (positive result) there is, however, still the possibility that the 

 organism is devoid of pathogenic properties and has been destroyed by 

 the normal peritoneal fluid. A control experiment should accordingly 

 be made with - 001 c.c, of normal serum in place of the anti-cholera serum. 

 If no alteration of the organism occurs with its use, then the conclu- 

 sion is that a true reaction has been given. Corresponding bacteriolytic 

 effects may be obtained by m vitro methods, introduced since Pfeiffer's 

 original method. ; 



