352 VETERINARY BACTERIOLOGY 



disease is most common in man and in the horse, although no 

 mammalia are immune. The disease is not transmitted by in- 

 gestion. The injection of the characteristic toxin is followed by 

 the symptoms of the disease. 



Character of Disease and Lesions Produced. The disease is a 

 typical toxemia. There is rarely, if ever, a general invasion of the 

 tissues. The organism remains localized at the seat of inoculation, 

 and produces the toxin which brings about the characteristic 

 symptoms. The entrance of the organism into a wound is not 

 always followed by the development of tetanus, for anaerobic 

 conditions must obtain, and it has been found that tetanus spores 

 entirely freed from toxin cannot germinate when introduced into 

 the tissues in moderate numbers. It is evident that the organism 

 has little initial pathogenic power. Usually considerable amounts 

 of dirt are introduced into the wound simultaneously with the 

 organism, and produce proper conditions for rapid development. 

 The tetanus toxin produced is absorbed, for the most part, by 

 the end-organs of the motor nerves, and travels to the nerve-cells 

 of the central nervous system by way of the axis-cylinders of the 

 peripheral nerves. Possibly a part of the toxin may be carried 

 to the central ganglion-cells by the blood-stream. The inoculation 

 period noted is believed to be due to the time required for the toxin 

 to pass along the nerves. That the toxin has a special affinity for 

 nervous tissue, and may be bound by it, has already been noted 

 in the discussion of toxins and antitoxins. The period of incuba- 

 tion in man averages about nine or ten days. In the horse it 

 varies from four to twenty days. Under exceptional conditions 

 this period may be much longer. Mortality is over 90 per cent, 

 when there is a short period of incubation, and over 50 per cent, 

 where the period is prolonged. The characteristic symptom in all 

 animals is a tetanus or stiffening of the muscles. The muscles at 

 the site of inoculation are generally the first, and, in mild cases, 

 they may be the only ones, affected. In the horse the appearance 

 of the tetanus or lockjaw, the retraction of the eyes and protrusion 

 of the nictitating membrane, spasmodic contraction of other mus- 

 cles of the head, and those of other parts of the body, arc diagnostic. 

 A postmortem examination usually shows absence of gross lesions. 

 Certain degenerative changes in the motor cells of the cord may 



