Natural immunity against toxins 335 



experimental control by Vaillard 1 , and specially in connection with 

 tetanus in the fowl. The blood or blood serum of these birds, when 

 mixed in varying doses, small, medium, and large, with tetanus toxin, 

 was never found to be capable of preventing susceptible animals 

 (mice, guinea-pigs, rabbits) from contracting tetanus : these animals 

 so treated behaved just as did the controls inoculated with toxin 

 only. 



The great resistance of the fowl against tetanus, one of the most 

 typical examples of natural immunity against a microbial poison, 

 cannot, therefore, be explained by the presence in the body fluids of 

 an antitoxin capable of neutralising and rendering innocuous the [352] 

 tetanus toxin. On the other hand, we are not justified in attributing 

 it simply to the absence of corresponding receptors in the sensitive 

 nerve cells. Since the fowl readily contracts tetanus when the toxin 

 is injected directly into the brain or when the fowl is weakened by 

 cold, it is evident that the sensitive elements never fail to absorb and 

 fix any poison that is presented to them. In ordinary cases, however, 

 when the fowl exhibits its remarkable resisting power against the 

 toxin injected in very large quantity, subcutaneously, into the muscles 

 or into the peritoneal cavity, the poison does not reach the sensitive 

 cells, being arrested and rendered innocuous whilst circulating in the 

 tissues of the organism. 



Yon Behring 2 is of opinion that in examples of natural immunity, 

 such as the one just examined, the principal cause of the refrac- 

 tory condition depends upon the impermeability to the toxin of the 

 capillary wall of the vessels. It is, however, difficult to maintain this 

 thesis in regard to tetanus in the fowl, when it is remembered how 

 readily tetanus toxin passes through filters and membranes, and 

 especially in view of the fact that weakening of the fowl by means of 

 cold renders it susceptible to doses of toxin which are tolerated 

 without inconvenience by normal fowls. 



We are, therefore, compelled to place the natural immunity of the 

 fowl against tetanus toxin in the category of cell immunities. This 

 toxin, as we have said, must be arrested en route before it reaches the 

 cells of the nerve centres. But where and how does this beneficent 

 arrest take place? Ten years ago Vaillard demonstrated that the 



1 Compt. rend. Soc. de Mol, Paris, 1891, p. 462; Ann. de VInst. Pasteur, Paris, 

 1892, t VI, p. 229. 



2 Article : Infectionsschutz und Immunitat in Eulenburg's " Real-encyclopadie 

 d. ges. Heilkunde" (Encyclop. Jahrbiicher), Wien, 1900, Bd. IX, S. 203. 



