INFECTIOUS DISEASES. 101 



Give the aetiology. 



The virus is produced by a bacillus which occurs in the earth, 

 in putrefying fluids, and in manure. 



Some cases occur without any apparent wound, and these cases 

 have received the name of idiopathic tetanus. 



In other cases it may follow wounds, especially punctured 

 wounds of the feet, where the plantar cushion is involved; those 

 wounds that seem trifling are more apt to be followed by tetanus 

 (called traumatic tetanus) ; also, where foreign bodies become 

 lodged, such as small splinters of wood. 



It may follow castration or other operations, as docking the 

 tail ; also, fracture of the vertebrae ; or it may follow small wounds 

 or abrasions from the harness. 



The tetanus bacillus can be isolated and cultivated, it growing 

 at the ordinary temperatures. 



It consists of a slender rod with rounded ends, and may grow 

 into long threads, and is anaerobic. 



The bacilli develop at the site of the wound. 



What is the morbid anatomy? 



There are no characteristic lesions found in the brain or in 

 the spinal cord. Congestions occur in different portions of the 

 nervous system. 



What is the semiology? 



Usually ten days after a wound the symptoms may show them- 

 selves, there being slight stiffness of certain muscles of the neck, 

 and possibly some difficulty in mastication. 



The rule is that the symptoms come on suddenly; the man 

 goes to feed the horse in the morning and finds he will not eat, 

 and that he seems stiff. 



The head is extended, the nose in the air, the tail slightly ele- 

 vated and carried to one side, the hind legs more or less stiffened 

 and wide apart (a straddling gait), and in severe cases the anterior 

 extremities are separated. In moving, the body is not flexed, the 

 animal moving as though he was made of one piece. 



There is difficulty in backing, the horse appears nervous, ex- 

 citable, and when you move him around quickly or elevate the head 

 the membrana nictitans is thrown over the eye. 



Trismus is often present, the teeth become set, and you cannot 

 introduce your finger or even a blade of a knife between them 



