IMMUNITY 457 



usually being | c.c. per 100 gnu. weight). The symptoms 

 i-lust-ly resemble those obtained by Pfeiffer. They found that 

 the toxicity of the filtrate was not altered by boiling, appar- 

 ently this toxic substance is different from Pfeiffer's endotoxin. 

 Within recent times numerous attempts have been made to 

 procure toxic fluids by disintegrating the cholera spirilla, e.g. 

 by methods of grinding, by solution by alkali, by autolysis, etc., 

 and a certain measure of success has been reached. There has 

 also been much discussion as to whether the toxic bodies 

 obtained are merely liberated endotoxins or whether they 

 also represent true extracellular toxins. The true relations 

 of these bodies has not yet been determined, but it would seem 

 that in all probability 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 circumstances the 

 spirilla undergo a granular transformation and, ultimately, 

 solution; this phenomenon is generally known as Pfeiffer's 

 reaction, and was applied by him to distinguish the cholera 

 spirillum from organisms resembling it. The following are the 

 details : 



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

 organism to be tested is added to 1 c.c. 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 gnu. in weigbt), and 

 the peritoneal fluid of this animal (conveniently obtained by means of 

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

 scopically alter 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 



