TETANUS 53 



that incubation is longer in direct proportion to the 

 size of the animal and the consequent length of the 

 nerves. In horses and cattle the symptoms are 

 exhibited after an incubation period of five days; 

 in smaller animals two to four days ; but in all cases 

 the incubation period may be very variable. The 

 more rapid the onset, the more acute are the 

 symptoms, and the more grave the prognosis. 



The poison of tetanus gradually loses strength on 

 keeping, and is not destroyed by heating to 135° C. 

 for ten minutes ; but its potency is rapidly destroyed 

 by sunlight. The poison contains two toxins, tetano- 

 spasmin, which produces spasms of the muscles, and 

 tetanolysin, which causes hemolysis of the red blood 

 corpuscles. Tetanus toxins have a great affinity for 

 the nervous system. Wassermann and Takaki have 

 shown the great affinity of the poison for brain tissue ; 

 they found that if they made an emulsion of brain 

 substance and mixed this with the toxins before 

 injections into animals no ill-effects were produced. 

 A protective influence was exercised even if the 

 emulsion was injected at a different point from the 

 toxin, without previous mixture. Cerebral substance 

 thus acts as an antitoxin to the poison — in other words, 

 the toxin has the power of combining with the side- 

 chains of the cerebral cells. When, therefore, these 

 cells are injected into another animal, they are 

 capable of uniting with the free poison and so 

 preventing it from attacking the living tissues of the 

 animal. 



