AXATOMICAL FEATURES. — SYMPTOMS. 319 



that of softness and want of textural cohesion. In the brain 

 and spinal cord Ave meet with serous effusion in the sub- 

 arachnoid spaces, or else an infiltration of the membranes 

 and connective-tissue belonging to these structures, with a 

 slightly coloured gelatinous material. 



These effusions and tissue-changes of the great nerve-centres 

 are variable as regards their situation, as also in the matter of 

 their extent and of the amount of the fibrillating matter pre- 

 sent, but invariable as to their character ; that is to say, they 

 are always purely serous or of a gelatinous hyaline material, 

 distributed throughout, or in connection with, the membranes. 



Symptoms. — The diagnostic symptoms are the excessive 

 urination, immoderate thirst — polydipsia — and impaired or 

 depraved appetite. In addition to these, which sufficiently 

 distinguish the disorder from every other, we have several less 

 important, not so attractive, and probably more variable as to 

 their appearance. The mucous membranes are pallid or dirty 

 coloured, the mouth clammy and sour-smelling, the hair want- 

 ing the close, sleek character of full health and vigour, and 

 the skin occasionally scurfy ; the pulse, whether frequent or 

 infrequent, is always wanting in volume and tone, while, if put 

 to any exertion, there is evident weakness, and a disposition to 

 perspire. Very often the appearance of the great diagnostic 

 features are not what first draw attention to the horse ; he may 

 have simply shown indications of not thriving by want of 

 vigour and sprightliness when at work, by excessive perspiration, 

 or by the existence of a depraved appetite, an inclination to 

 swallow foul material and to refuse his usual food. 



Very shortly, however, the immoderate thirst and excessive 

 urination appear, and as these become developed the other 

 symptoms are more confirmed. The amount of urine voided 

 is generally increased, and characterized — particularly when 

 the causes seem to be exogenous — by the paleness of its 

 colour and low specific gravity. This is accounted for from 

 the excess of water, the absence or relatively small amount 

 of the earthy carbonates, and, it is said,' by the presence of free 

 acetic acid. Ordinaril}^, horses' urine has the specific gravity 

 of from 1035 ; in this condition it is often seen at 1003. 

 However, it has been said — we have not tested the truth of the 

 statement — that the quantity of solid matter voided in a given 



