556 • DISEASES OF THE HORSE. 



infectious, and that it can not be transmitted by blood inoculations, 

 but is conveyed with remarkable ease by ticks coming from diseased 

 cattle. That the cause has not been observed may be accounted for 

 by its being invisible even to the high magnification of the microscope. 

 On some farms and in some stables bighead is quite prevalent, a 

 number of cases following one after another. On one farm of thor- 

 oughbreds in Pennsylvania all the yearling colts and some of the aged 

 horses were affected during one year, and on a similar farm in Vir- 

 ginia a large proportion of the horses for several years were diseased, 

 although the cows and sheep of this farm remained unaffected. 



SYMPTOMS. 



The commencement of the disease is usually unobserved by the 

 owner, and those symptoms which do develop are generally not well 

 marked or are misleading unless other cases have been noted in the 

 vicinity. Until the bones become enlarged the symptoms remain so 

 vague as not to be diagnosed readily. The disease may be present 

 itself under a variety of sj^mptoms. If the bones of the hock become 

 affected, the animal will first show a hock lameness. If the long bones 

 are involved, s3^mptomsof rheumatism will be the first observed, while 

 if the dorsal or lumbar vertebra3 are affected indications of a strain of 

 the lumbar region are in evidence. Probabl}^ the first symptom to be 

 noticed is a loss of vitality combined with an irregular appetite or 

 other digestive disturbance, and with a tendency to stumble while in 

 action. These earlier symptoms, however, may pass unobserved, and the 

 appearance of an intermittent or migrator}^ lameness without an}^ visi- 

 ble cause may be the first sign to attract attention. This shifting and 

 indefinite lameness, involving first one leg and then the other, is very 

 suggestive, and is even more important when it is associated with a 

 tendency to lie down f requentl}^ in the stall and the absence of a desire 

 to get up, or the presence of evident pain and difficulty in arising. 



About this time, or probabl}^ before, swelling of the bones of the 

 face and jaw, which is almost constantly present in this disease, will 

 be observed. The bones of the lower jaw are the most frequently 

 involved, and this condition is readil}^ detected with the fingers by the 

 bulging ridge of the bone outside and along the lower edge of the 

 molar teeth. A thickening of the lower jawbone may likewise be 

 identified by feeling on both sides of each branch at the same time 

 and comparing it with the thinness of this bone in a normal horse. 

 As a result mastication becomes difficult or impossible and the teeth 

 become loose and painful. The imperfect chewing which follows causes 

 balls of food to form which drop out of the mouth into the manger. 

 Similar enlargements of thebones of the upper jaw ma}^ be seen, caus- 

 ing a widening of the face and a bulging of the bones about midway 

 betW'Cen the eyes and the nostrils. In some cases the nasal bones also 



