166 BACTERIA IN RELATION TO DISEASE 



These arguments, it is true, do not give anything like a complete 

 explanation of the phenomena, but they show how far we can go without 

 assuming the existence of specific antitoxines, using in their place the 

 phenomena of toleration, phenomena which are, it is true, still unexplained. 



As soon as we grant the existence of antitoxines, another mysterious 

 property of the organism has to be assumed, namely the ability to produce 

 a specific antitoxine for each kind of toxine, and possibly for every other 

 poison. Theoretical medicine is at present strongly inclined to explain 

 immunity and serum therapeutics by such antitoxines. By the incorpora- 

 tion of poisons the body is stimulated to produce antidotes ; these increase 

 as immunity increases, and are the effective agents in the serum. Serum 

 therapeutics and serum immunity consist in the introduction into the 

 organism of ' anti-substances.' These substances are, as we have seen, as 

 yet quite unknown, and opinions are divided as to their manner of action, 

 whether they neutralize the poison by chemical combination or only 

 stimulate the body to greater resistance. 



The theory of ' anti-substances ' is also involved in the terminology 

 which is used by Behring and Ehrlich (158) to designate the various 

 strengths in which the diphtheria serum is sold. By a ' normal ' toxine is 

 understood a filtered virulent diphtheria bouillon culture of which 0-3 c.c. 

 suffices to kill a one-kilo, guinea-pig when injected subcutaneously. For an 

 animal of from 200 to 300 grm. o-i c.c. would be enough. A normal anti- 

 toxic unit is a solution of antitoxine of which o-i c.c. destroys the virulence 

 of i c.c. normal toxine, i.e. sufficient to protect a guinea-pig from ten times 

 the fatal dose. This of course can only be determined by experiments on 

 animals, toxine and antitoxine being injected together. Therefore to make 

 a guinea-pig immune against the lethal dose of 01 c.c. normal toxine, 

 o-oi c.c. of the normal antitoxine is necessary. Normal serum contains in 

 i c.c. one ' antitoxic unit/ and therefore i c.c. of such a serum is sufficient 

 to protect ten guinea-pigs against the fatal dose (157). 



The therapeutical and clinical questions involved in the serum treat- 

 ment cannot of course be discussed here. A mature and final judgement 

 as to its efficacy will not be possible for many years (159). 



A theoretical explanation of the phenomena of immunity is rendered 

 very difficult by the distinction that has been supposed to exist between 

 bactericidal and antitoxic action. While it is generally admitted that pro- 

 tection from diphtheria and tetanus is caused by ' antitoxines,' that is to say, 

 by substances that destroy the poison of the bacilli, it is asserted that in 

 artificial immunity against cholera, typhoid, and some other diseases, the 

 chief part is played by bactericidal substances. The bactericidal effect is 

 said to be specific in each case. Pfeiffer's cholera-serum reaction, the 

 meaning of which is at present the subject of a good deal of discussion, 

 may here serve as an example of these phenomena (160). 



