The Urine. 201 



The Total Solids of the urine consist of organic and in- 

 organic matter, of which 5 ozs. are organic and 3 ozs. in- 

 organic ; they are liable to great variation, sometimes being 

 found to be considerably in excess of that mentioned. 



The total solids are considerably affected by the diet. 

 E. Wolff* found that Avhen he reduced the hay and increased 

 the corn ration, the solids in the urine decreased ; thus, on 

 a diet of 17"6 lbs. hay and 4'4 lbs. oats the urinary solids for 

 24 hours amounted to 20 ozs., whilst on a diet of 8\S lbs. 

 hay, 13 - 2 lbs. oats, the total solids fell to lGj ozs. 



Urea is the chief end product of proteid change ; it re- 

 presents the wear and tear of proteid tissues, but is not, as 

 we shall see in another chapter, a measure of the work pro- 

 duced. The amount of urea excreted daily is about 3f ozs. 

 Half the weight of urea consists of nitrogen. The sources 

 of urea have given rise to considerable discussion ; it was 

 supposed to originate in the muscles, but muscular substance 

 only contains a trace of urea, if any. It is considered that 

 it may be formed in two or three ways : 1. From the nitrogen 

 of the food split off during pancreatic digestion in the 

 form of leucin and aspartic acid, bodies known as the amido 

 acids. 2. But these amido acids do not account for all the 

 urea, and it is supposed that the ammonia and carbonic acid 

 split off from the proteid molecule subsequently combine to 

 form urea. 3. It is possible that creatin, a substance which 

 exists largely in muscle, may undergo conversion into urea. 



In whatever way urea is formed the seat of the change is 

 principally in the liver, while probably the spleen and lym- 

 phatic glands may participate (Halliburton). 



The origin of urea from ammonium carbonate is an inter- 

 esting practical point, and one worth bearing in mind in 

 the case of a patient receiving this drug medicinally, in 

 examining the urine in disease for excess of urea. 



Uric Acid does not, in my experience, occur in the urine 

 of the horse excepting as the result of disease, and prac- 

 tically we may regard uric acid in herbivora as replaced by 

 hippuric acid, though the latter is at once replaced by uric 

 * Ellenberger's % Physiologie.' 



