264 PHYSIOLOGY AT THE FARM. 



the products of the living solids by disintegration, and the 

 base of such salts may be either ammonia originating in that 

 disintegration, or potash and soda taken in with the food, com- 

 bined with citric, tartaric, oxalic, or other organic acids, these 

 acids in the living system being changed into carbonic acid to 

 be eliminated for the most part in respiration. Potash and soda, 

 particularly potash, abound in the food of herbivorous animals, 

 and therefore the alkaline sulphates and phosphates abound 

 especially in their urine ; but being deficient, for the most 

 part, in the food of carnivorous animals, they are replaced in 

 the urine of such animals by a larger proportion of ammonia. 



The following passage from Dr Carpenter's work on Com- 

 parative Physiology affords a good summary of what is known 

 further of the urinary function : " Although the relations of 

 the amount of the organic compounds in the urine to food, 

 exercise, &c., have been as yet studied almost entirely in the 

 human subject, there can be no reasonable doubt that the 

 same general rules will be found to hold good elsewhere. The 

 proportion of urea which is voided in a given time is propor- 

 tional, cceteris paribus, to the amount of muscular exertion 

 that has been put forth, showing that its presence depends 

 in part upon disintegration of the muscular tissue. But this 

 is not its sole source, for it is greatly augmented also by an 

 excess of azotised compounds in the food these compounds, 

 as already shown, not being applied to the nutrition of the 

 muscular substance, unless a demand for augmented formation 

 has been created by previous functional activity. Thus the 

 average proportion of urea in the human urine, under ordinary 

 circumstances as to food and exercise, appears to be from about 

 20 to 35 parts in 1000, but may be raised to 45 parts by 

 violent exercise, and to 53 parts by an exclusively animal 

 diet ; whilst it may fall as low as 15 or even 12 parts when 

 the diet is deficient in azotised matter. The average daily 



