TETANUS. 529 



Wounds in the intestines (for instance, by worms) are probably the usual 

 points of entrance of these microbes, whcu the disease is conveyed by means 

 of food or water. 



PERIOD OF INCUBATION. — " The period between the intro- 

 duction of the germs of tetanus and the appearance of the first 

 symptoms is very variable. Its average duration is fifteen days. 

 Hofi'man saw tetanus set in six hours after a prick in the foot of 

 a horse. Usually it develops between the second and thirtieth 

 day " (Carougeau). Professor McFadyean (" Journal of Conip. 

 Path.," Sept., 1897) states : " In natural tetanus occurring in a 

 wound infection, the period of incubation is seldom less than a 

 week." 



MORTALITY. — According to Carougeau, the percentage of mor- 

 tality varies from 70 to 75. 



THE CHANCES OF RECOVERY vary according to the length of 

 the period of incubation. If that period is short, death is almost 

 certain. Also, the more acute the attack, the less hope will there 

 be of recovery. Tetanus is much more fatal in young animals, 

 and especially in foals, than in old horses. We may hope for the 

 best, if after nine or ten days, the patient is doing fairly well. 



DURATION OF ATTACK.— Tetanus generally runs its course 

 in from three days to six weeks. 



SYMPTOMS. — The muscles that are usually first brought under 

 the influence of the continual spasm of tetanus are those of ex- 

 pression, which, when thus affected, give the face a pinched or drawn 

 appearance. The other muscles of the head and those of the neck 

 soon follow. Hence, we have the mouth closed, the nose poked out, 

 the head elevated, and the neck "ewed" (from contraction of the 

 levator humeri). The muscles of breathing and those of the limbs 

 become contracted so that the back is hollowed and the tail raised, 

 and the horse stands with out-stretched limbs. He shows great stiff- 

 ness and rigidity in attempted movement. The eyes are sunk, and, 

 during excitement, as when a person startles the horse, the haws 

 are quickly protruded and then withdrawn. The animal looks ner- 

 vous and terrified. The nostrils are dilated, the breathing 

 quickened, and the flanks tucked up and heaving, which symptoms 

 are due to the fact of the muscles of the chest becoming fixed, so 

 that breathing has to be carried on almost entirely by the action of 

 the diaphragm. As this abdominal breathing can be maintained 

 for only a short time, we generally find that cases of tetanus which 

 are rapidly fatal, are those in which spasm of the muscles of the 



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