TOXINS OF THE TETANUS BACILLUS 439 



the dog about 500, the rabbit 1800, the cat 6000, the goose 

 12,000, the pigeon 48,000, and the hen 360,000. 



A striking feature of the action of tetanus toxin is the 

 occurrence of a definite incubation period between the introduc- 

 tion of the toxin into an animal's body and the appearance of 

 symptoms. The incubation period varies according to the species 

 of animal employed, the path of infection, and the dose given. 

 In the guinea-pig it is from thirteen to eighteen hours, in the 

 horse five days, and the incubation is shorter when the poison is 

 introduced into a vein than when injected subcutaneously. In 

 man the period between the receiving of an injury and the 

 appearance of tetanic symptoms is usually from two to fourteen 

 days, but this period may be lengthened, and there is some 

 evidence that the bacilli may remain a considerable time shut 

 up in the body before producing effects. 



With regard to the action of the toxin, it has been shown to 

 have no effect on the sensory or motor endings of the nerves. 

 It acts solely as an exciter of the motor cells in the spinal cord, 

 the nerve storm being often precipitated by peripheral irritation. 

 The motor cells in the pons and medulla are also affected, and 

 to a much greater degree than those in the cerebral cortex. 

 When injected subcutaneously the toxin is absorbed into the 

 nerves, and thence finds its way to that part of the spinal cord 

 from which these nerves spring. This explains the fact that in 

 some animals the tetanic spasms appear first in the muscles of 

 the part in which the inoculation has taken place. This is not 

 the case with man, in whom usually the first symptoms appear 

 in the neck. After subcutaneous injection of toxin, part finds 

 its way into the blood stream, and if infected animals be killed 

 during the incubation period there is often evidence of toxin in 

 the blood and solid organs. In the guinea-pig there is little 

 doubt that tetanus toxin has an affinity solely for the nervous 

 system. In other animals, e.g., the rabbit, an affinity may exist 

 in other organs, and the fixation of the poison in such situations 

 may give rise to no recognisable symptoms. In such an animal 

 as the alligator, it is possible that while some of its organs have 

 an affinity for tetanus toxin its nervous system has none. 

 In this connection great controversy has arisen regarding the 

 observations of Wassermann and Takaki that tetanus toxin can 

 be absorbed by emulsions of the brains of susceptible animals. 

 The facts are of great scientific interest, and a possible explana- 

 tion of them will be discussed in the chapter on Immunity. 

 If tetanus toxin be introduced into the stomach or intestine, it 

 is not absorbed, but to a large extent passes through the intestine 



