THE TOXINS 163 



Penetration of the Body. To reach the sensitive cells 

 the toxins do not always follow the same path. Injected 

 subcutaneously they pass into the lymph, then into the blood. 

 Injected into the blood they save time, since the passage 

 through the lymph is avoided. Introduced into the alimentary 

 canal the botulismus toxin retains its potency, but the 

 diphtheria toxin and the tetanus toxin are inactive even after 

 being swallowed in much more than a lethal dose. This 

 destruction or neutralization cannot be attributed to an action 

 peculiar to the intestinal epithelium nor to any extent to the 

 influence of the bacteria and their fermentations in the 

 digestive tube, but chiefly to the action of the digestive 

 secretions, the pepsin, and above all the pancreatic juice. 



According to the experiments of Meyer and Ransom and of 

 Marie and Morax, the tetanus toxin does not pass directly from 

 the site of inoculation to the nerve centres ; it penetrates the 

 peripheral nerves at their motor terminations, and follows these 

 nerves to reach the centres. All three species of nerve fibre, 

 motor, sensory, and sympathetic, can carry it ; but the carrying 

 power of the nerve depends absolutely on the integrity of the 

 axis cylinder. By employing antitoxin it is possible to localize 

 the action of the toxin to certain definite territories and paths. 

 Dissociation experiments have shown that the antitoxin acts 

 by neutralising the toxin still in circulation, but is no longer 

 capable of neutralising toxin absorbed by the nerve trunks 

 (these do not absorb antitoxin). The fact that in certain 

 animals, man and the horse, tetanus always begins by a con- 

 traction of the muscles of the jaw (" lockjaw ") only means 

 that even after a stab or a wound at the end of a limb sufficient 

 toxin passes sufficiently quickly into the circulation to affect 

 the centres on which the innervation of these muscles 

 depends. 



The cells of the central nervous system are sensitive to 

 many poisons, whether these reach them by the nerve filaments 

 or through the blood. Directly introduced into the centres 

 the poisons act in a smaller dose, and often produce different 

 symptoms from poisons injected subcutaneously or into the 



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