114 MANUAL OF EQUINE MEDICINE. 



conditions, that although usually a sporadic affection, it 

 occasionally develops truly enzootic characters (Robertson). 



Etiology. — It is probably caused by disordered condition 

 of the vaso-motor centres, leading to dilation of the renal 

 vessels, and thus causing polyuria. The disordered innerva- 

 tion is probably due to defective assimilation, brought about 

 by improper diet or by causes peculiar to the locality. 



Mouldy hay, musty, damp, or kiln-dried oats, and bad 

 corn, are fertile sources of the disease. Boiled food is also 

 sometimes a cause of diabetes insipidus. In some cases 

 the disease may come on in the absence of such causes, and 

 it is then of a most severe type, and usually due to mal- 

 assimilation of food and other causes, such as prolonged 

 exertion and exposure to cold. 



During convalescence from some debilitating diseases, 

 even slight dietetic errors may induce polyuria. 



Symptoms. — Excessive urination, great thirst, anorexia 

 or depraved appetite, are the diagnostic symptoms. The 

 mouth has a sour, unpleasant odour, and the skin is scurfy. 

 The pulse varies in number, but the volume is diminished 

 and the tone deficient. The visible mucous membranes are 

 pale, and the animal is enfeebled and perspires on slight 

 exertion. The urine voided is pale, of low specific gravity, 

 from 1002 to 1003, but the total amount of solids is pro- 

 bably not diminished. According to Lassaigne, it contains 

 free acetic acid, and alkaline carbonates are absent. When 

 this form of diabetes follo\ys some debilitating disease, the 

 urine is of higher specific gravity, and the debility and 

 wasting are more marked. 



When the disease continues unchecked, the animal 

 gradually loses strength, becomes emaciated, and structural 

 changes follow in many organs. Dropsical effusions into the 

 serous cavities and the lax connective-tissues are then of 

 common occurrence. 



