306 INFECTIOUS DISEASES 



The specific cause is a pin-shaped germ, the Bacillus tetani 

 (Fig. 110), that is present in the soil, especially those that are 

 rich and well manured. The germ enters the body by way of 

 a wound, especially punctured wounds. Infection may take 

 place through some wound in the mucous membrane lining the 

 mouth, or other parts of the digestive tract. Infection may 

 follow a surgical operation, such as castration. In any case, 

 the germ requires an absence of air (oxygen) for its development. 

 The period of incubation varies from one to two weeks, the 

 length of time depending on the nearness of the wound to a large 

 nerve trunk or brain. 



The first symptom observed is a stiffness of the muscles, 

 especially those nearest the point of in- 

 oculation or wound. The muscles of 

 the head, neck, back and loins are often 

 affected first, and when pressed upon 

 with the fingers feel hard and rigid. 

 The disease rapidly extends, producing 

 spasms of other muscles of the body. 

 In breathing, the ribs show less move- 

 ment than normal, the head is held in 

 Fig. no.—BacUius tetani. qj^q positiou and higher than usual, 

 the ears are stiff or pricked, the nostrils dilated, the lips rigid or 

 drawn back and the eyes retracted, causing the " third eyelid " 

 to protrude over a portion of the eye (Fig. 111). In most cases 

 the muscles of mastication and swallowing are affected. The 

 animal may be unable to open its mouth and swallows with 

 difiiculty. AMien standing, the limbs are spread out so as to 

 increase the base of support, and in acute cases about to ter- 

 minate fatally, the pulse is quick and small and the respiration 

 shallow, rapid and labored. The animal sweats profusely, falls 

 down and struggles violently, but remains conscious to the end. 



In the subacute form (Fig. 112) the symptoms are mild, 

 and the animal may be able to move about, eat and drink without 

 very great effort. 



