334 Prof. F. Smith. [June 20, 



The animal was worked from the 14th until the 24th March, and' 

 again on the 26th and 28th March. 



Urine of Work. 



Total nitrogen. Urea. 



25th March 16 *324 grams. 30 -25 grams. 



27th „ 25-725 „ 52 '25 „ 



29th „ 23-000 „ 47-50 „ 



The table clearly shows us how variable is the excretion of nrea in 

 spite of the fact that the diet remained the same ; it is evident that 

 the nrea in horses is no more a measure of the muscular waste than 

 it is in man. Kellner's experiments* are remarkably complete. He 

 made horses produce a definite amount of work ; the experiment was 

 divided into five periods : — 



Work produced. Nitrogen produced. 

 1st Period .... 475,000 kilogrammeters 99 - grams. 



2nd „ .... 950,000 „ 109-3 „ 



3rd „ .... 1,425,000 „ 116 -8 „ 



4th „ 950,000 „ 110-2 „ 



5th „ .... 475,000 „ 98-3 „ 



Here we have a slight increase in the output of nitrogen, quite 

 insufficient to account for the increased work produced. 



Hippuric Acid. — Owing to the statement made by Liebig that 

 benzoic acid was found in the urine of working horses, and hip- 

 puric in the urine of those which rested — a statement which has often 

 been repeated since his time, and almost formulated into the doctrine 

 that benzoic was present in the horses of the poor, whilst hippuric 

 predominated in that of the wealthy — I have been at great pains 

 to discover what element of truth the doctrine contained. 



The method employed for the determination of benzoic and hip- 

 puric acids was the following : — • 



The urine is treated with excess of milk of lime, filtered, evaporated 

 to one-fifth of its bulk, and acidified with HC1. If hippuric acid be 

 present it forms in some cases almost immediately, but in the majority 

 it has to stand from twelve to twenty-four hours ; if benzoic be 

 present it forms almost at once. Both acids are in a highly impure 

 condition, the hippuric (in black seaweed-like masses) is dissolved in 

 water, boiled, and, whilst boiling, a current of chlorine gas passed 

 through it to destroy the organic matter ; it is then filtered hot, and 

 deposits pure hippuric acid in fine needles in the course of a few 

 hours. The impure benzoic is filtered, the solid residue collected in 



* ' Landw. Jakrbucher,' 1879. 



