426 TETANUS 



a vein than when injected subcutaneously. In man the period 

 between the receiving of an injury and the appearance of tetanic 

 symptoms is from two to fourteen days. 



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 reflex excitability of the motor 

 cells in the spinal cord. 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 subcutaneoitsly 

 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.(j. 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. These facts are of great scientific 

 interest, and a possible explanation 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 unchanged. Evidence that any 

 destruction takes place is wanting. 



Within recent years some important light has been shed on 

 the mode of action of tetanus toxin. Marie and Morax studied 

 the path of absorption when the toxin was injected into the 

 muscles of the hind limb. The sciatic nerve in a rabbit was cut 

 near the spinal cord and toxin introduced into the muscles of the 

 same side ; after some hours the nerve was excised and introduced 

 into a mouse the animal died of tetanus. But if the nerve were 

 cut near the muscles and the same procedure adopted, the mouse 

 did not contract the disease, though no doubt the cut nerve had 

 been surrounded by lymph containing toxin. If the same 

 experiment were performed and an excess of toxin injected into 

 the other limb, still only the nerve which was left in connection 

 with the muscle showed evidence of the presence of toxin. From 

 this it was deduced that the toxin was absorbed by the end- 



