120 BACTERIOLOGY FOR NURSES 



of natural antitoxin in the blood. A minute amount of toxin 

 (about one fifth of the minimum lethal dose for a guinea pig) 

 is injected intradermically. If the person receiving the toxin 

 possess an amount of antitoxin equal to at least one thirtieth of a 

 unit in each cubic centimeter of blood the injected toxin is neu- 

 tralized and no reaction appears ; if, on the other hand, he has no 

 antitoxin, the toxin acts as an irritant to the skin and in from 

 twenty to forty-eight hours produces a small inflamed area. This 

 positive reaction indicates that the person has no natural antitoxin 

 and therefore that he is susceptible to the disease ; conversely, a 

 negative reaction indicates that an individual has in all probability 

 sufficient natural antitoxin to protect him, even in case of exposure, 

 and a prophylactic dose is unnecessary. 



Tetanus Toxin. Tetanus, like diphtheria, is a local infection 

 characterized by a general toxemia. The bacilli and spores never 

 gain access to the blood ; they remain at site of infection where 

 they produce their toxin, which when absorbed is responsible for 

 the disease. The blood, then, usually contains tetanus toxin, but 

 is sterile so far as the organisms are concerned. Two different 

 poisonous substances have been shown to exist in tetanus toxin : 



(1) tetanospasmin, which has a special affinity for nerve tissue and 

 to the action of which the characteristic symptoms are due, and 



(2) tetanolysin, a substance of probably much less importance 

 which attacks the red blood corpuscles, ruptures the envelope, and 

 liberates the contents, giving rise to a more or less anemic condition. 



One of the greatest dangers of tetanus lies in the fact that 

 while the local lesion may show no sign of disturbance the central 

 nervous system may suddenly develop symptoms of poisoning. 

 The toxin is produced during or soon after the first twenty-four 

 hours and from the point of infection it passes rapidly into the 

 blood and lymph stream and according to certain authorities 

 is absorbed by the end plates of the motor nerves and quickly 

 travels along the axis cylinders to the spinal cord. The more gen- 

 eral opinion, however, is that the toxin passes by way of the lym- 

 phatics of the nerves and not by way of the axis cylinders. So 

 great is the affinity of tetanus toxin for nerve tissue that once 



