SOME COMMUNICABLE DISEASES 371 



certain soils and in mold on horse manure. Man and the horse 

 possess great susceptibility for virulent cultures. Sheep and 

 swine are also susceptible. Infection occurs through wounds of 

 the hoof, or of the skin made by nails, fork tines, splinters, or 

 infected surgical instruments. In one case a piece of burlap was 

 used to cover the crupper strap which had galled the skin under 

 the tail. Shortly the burlap gathered a quantity of feces con- 

 taining tetanus bacilli which were rubbed into the skin and pro- 

 duced tetanus from which the animal died in ten days. The 

 incubation period is usually from one to two weeks but may be 

 shorter. 



Symptoms. — The animal shows violent spasms of groups of 

 body muscles from one to twenty days after inoculation. When 

 those of mastication are affected the jaws become immovable. 

 This has given rise to the term "lockjaw." The ears, tail, and 

 limbs stiffen. Chief among the diagnostic symptoms in the horse 

 is the protrusion of the membrana nictitans, or "haw," over the 

 eyeball when the head is raised. A stilty attitude is assumed and 

 a stiff gait when in motion. Sweating is common in severe 

 cases. In swine the disease often occurs after ringing and cas- 

 tration and is. accompanied by marked trismus. 



Treatment. — In mild cases given prompt treatment recovery 

 may be expected. Thorough disinfection of the seat of infection 

 is the first essential in treatment. Quiet quarters and provision 

 for comfort are of greater importance than drugs. Injections 

 of antitetanic serum, produced by injecting horses with increasing 

 doses of tetanus toxin, protect the animal, if given early. The 

 serum treatment is of slight value after the symptoms of tetanus 

 have become well marked. A postmortem examination of ani- 

 mals dead from tetanus is usually negative. 



TUBERCULOSIS 



Tuberculosis is a communicable disease affecting man and 

 animals. From an economic viewpoint its occurrence in cattle 

 and swine is of most importance. In 1917 nearly 25 per cent, 

 of all hogs slaughtered in one city were found to be affected 

 with tuberculosis. Like other communicable diseases, it is both 

 infectious and preventable. It is characterized by the formation 

 in the internal organs of small nodules or tubercles that have a 

 tendency to become cheese-like and later calcified. 



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