THE TOXINS 167 



first, a destruction or neutralisation of the toxins by an anti- 

 toxin elaborated by the brain cells. The fixation can be 

 modified by altering the physical conditions : brain matter 

 emulsified in physiological saline solution (o'8 per cent.) is a 

 stronger fixative than the same emulsified in distilled water, 

 but ten times weaker than the same emulsified in salt solution 

 of 10 per cent. The brain gives up the toxin more or less 

 quickly and restores the toxicity to water when it is allowed to 

 macerate, and also after drying or digestion with papaine : the 

 toxin liberated has all the biological properties which it had 

 before its intimate contact with the brain matter. This 

 observation negatives the hypothesis of a secondary toxin 

 elaborated by the cells from the toxin received and capable of 

 acting immediately without incubation. 



It is because of this fixation property of the cells of the 

 body that the toxin injected disappears more or less rapidly 

 from the blood and cannot be recovered, or only in very small 

 degree, from the excretions. In the rabbit seventeen hours after 

 injection no free toxin is to be found either in the blood or in 

 the organs, and there is never any in the blood at the moment 

 when the tetanic symptoms commence (about forty-eight hours 

 after intravenous inoculation. A. Marie). 



Since the tetanus toxin may be fixed on cells other than the 

 nerve-cells, it is evident that the former keep back at least a 

 portion of the toxin, acting thus as a sort of screen to the 

 nerve-cells. For example, the rabbit is less sensitive to tetanus 

 than the mouse and the guinea-pig because its spleen fixes the 

 toxin and saves its brain. Hence it is not the power of 

 fixation in general which explains the sensitiveness of a 

 particular animal, but the selective fixation on certain definite 

 cells whose activity is indispensable to life, for example, the 

 cells of the medullary nuclei or of the sympathetic ganglia. 



Scorpions can stand very large doses of tetanus toxin 

 without symptoms ; the toxin rapidly disappears from the blood 

 and accumulates in the liver. The alligator, which is re- 

 fractory to tetanus, retains in its blood for more than a month 

 toxin which has been injected into it. The carp, the axolotl, 



