TETANUS. 513 



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. 

 A case is recorded in which tetanus set in six hours after a prick 

 in the foot of a horse. Usually it develops between the second and 

 thirtieth day. Pixjfessor Sir John McFadyean (" Journal of Comp. 

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

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

 week. 



MORTALITY. — The percentage of mortality ranges 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 hop© will 

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

 and especially in foals, than in old horses. Hope may be enter- 

 tained 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 usually first brought under the 

 influence of the continual spasm of tetanus are those of expression, 

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

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

 soon follow. The mouth is closed, the nose poked out, the head 

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

 humeri). The muscles of breathing and of the limbs become con- 

 tracted so that the back is hollowed and the tail raised, and the 

 horse stands with outstretched limbs. He shows great stiffness 

 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 are quickly protruded and then withdrawn.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 

 nervous 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, cases of tetanus which are rapidly fatal, are 

 those in which spasm of the muscles of the chest is a prominent 

 feature. Death may also quickly occur from continued spasm of 

 the muscles of the larynx. The symptoms generally come on 

 gradually. Although there is continued oramp of the muscles ; the 



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