Protective vaccinations 497 



receive a quantity of a living culture of diphtheria bacilli which kills [520] 

 control animals in 30 hours. The protective power of the serum 

 in relation to the weight of the animal is thus determined. For 

 example, a serum which is said to be active at 1/100,000 has the 

 power, in a quantity equal to l/100,000th of the weight of the 

 inoculated guinea-pig, of preventing a fatal result. It was thought, 

 at first, that the protective power, measured in this way, would 

 be proportional to the antitoxic property determined according to 

 Ehrlich's method. But as the results given by these two methods 

 were often widely different, it was resolved at the Pasteur Institute 

 to examine by both methods all the serums intended for use in 

 practice. This led to the conclusion formulated by Roux 1 , in his 

 report communicated to the International Congress of Hygiene, held 

 at Paris in 1900, that a serum possessing a very high protective 

 power (against the living diphtheria bacillus) might be only feebly 

 antitoxic, and vice versa. 



This result is explained by the fact that the antidiphtheria serums 

 are very complex fluids, containing several superposed properties 

 of very variable strength. Marx 2 , of the Frank fort-on-Main Institute, 

 tried to shake Roux's conclusions, bringing forward his experiments 

 made on guinea-pigs and rabbits injected with antidiphtheria serum 

 into the peritoneal cavity and into the veins. He wished in this way 

 to avoid the introduction of the serum into the subcutaneous tissues, 

 whence the absorption of the antitoxin must take place in a very 

 irregular fashion. In Marx's experiments, thus carried out, the 

 protective power of the serums was always found to run parallel with 

 their antitoxic power, from which he concluded that Roux's view 

 was incorrect. It must not be forgotten, however, that this view 

 was founded on experiments in which the antitoxin had been 

 injected into the subcutaneous tissue before or simultaneously with 

 the toxin or the diphtheria bacillus. Under these conditions the 

 protective power is often found to be altogether disproportionate to 

 the antitoxic power. This fact has been observed so carefully and with 

 such exactness that it is impossible to deny it. Xow it is undoubted 

 that the conditions of the experiments upon which Roux relies 

 correspond much more closely with those that are realised in 

 vaccination of man against diphtheria than with the conditions met 

 with in Marx's experiments. In these vaccinations antidiphtheria 



1 Compt. rend. X Congr. internat. d'hyg. et de demogr., Paris, 1900. 



2 Ztschr. d. Hyg., Leipzig, 1901, Bd. xxxvin, S. 372. 



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