440 TETANUS 



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- 

 plates in the muscle and not from the lymphatics surrounding 

 the nerve. It was further shown that a nerve in the process of 

 degeneration following section did not absorb toxin after the 

 manner of a normal nerve. By a similar method it was shown 

 that the absorption by the nerve was fairly rapid, as one hour 

 after injection the toxin was present in it, and from other 

 experiments the view was put forth that the toxin was centripetal 

 in its flow and did not pass centrifugally in a nerve to which it 

 artificially gained access. Further observations have been made 

 on this subject by Meyer and Ransom. These observers found 

 evidence that toxin is only absorbed by the motor filaments of a 

 nerve, for while tetanus could be produced by injection into a 

 mixed nerve like the sciatic, the introduction of a lethal dose into 

 such a sensory nerve as the infra-orbital was not followed by 

 disease symptoms. If a small dose of toxin be injected into the 

 sciatic nerve, it reaches the corresponding motor cells of the cord, 

 and a local tetanus of the muscles supplied by the nerve results. 

 With a larger dose the poison passes across the commissure to 

 the corresponding cells of the other side, and if still further 

 excess is present it passes up the cord to higher centres. The 

 affection of such higher centres can be prevented by section of 

 the cord. Meyer and Ransom hold that when toxin is injected 

 subcutaneously or intravenously, it only acts by being absorbed 

 by the end-plates in muscles and thence passes to the cord, and 

 they consider that the incubation period is to be explained by the 

 time taken for this extended passage to occur. In this connection 

 they point out that it is in the larger animals, where the nerve 

 path is longest, that the incubation period is also long. Like 



