CHEMICO-AGRICULTURAL TOUR. 141 



filled with stron£^ sulphuric acid, chloride of calcium, and caustic 

 potash ; all of which, previous to the commencement of the exper- 

 iment, had their weights accurately ascertained. A comparative 

 experiment was at the same time made with the air of the outer 

 apartment, in which this apparatus was placed. At the close of 

 the experiments, which were carried on for several hours, and in 

 some cases days, all the tubes were carefully re-weighed, and the 

 excess of increased weight in the sulphuric acid, chloride of calcium 

 and potash tubes, in the case of the air drawn through the appara- 

 tus, over that produced by the air of the outer apartment, indicated 

 (as is well known in chemical analysis) the amount of water and 

 of carbonic acid which had been exhaled from the lungs and skin 

 of the subject during the period the experiments were carried on. 

 The excretions, likewise, which were passed during the same pe- 

 riod being all carefully collected, and retained by a suitable 

 arrangement, their composition was afterwards ascertained by a 

 chemical determination of their constituents. 



In this way. Professors Bischoff and Fehling have very accu- 

 rately determined what portions of our food ultimately pass off by 

 the lungs and skin, and what are eliminated in the excretions, 

 which are points of much interest and practical importance. 1 

 have as yet been unable to see any published account of the results 

 of Professors Bischoff and Fehling's experiments with this appara- 

 tus ; but if I rightly understood Dr. Ranke, the German gentleman 

 who kindly took me to see the Physiological Institute, and showed 

 me this apparatus, their experiments led them to the following 

 conclusions, which confirm in different particulars the results of 

 Professor Haughton, of the Dublin University, and other gentle- 

 men who have previously investigated this subject: 



let. That the nitrogenous portions of the food went to repair the 

 conjtinuous waste of the nitrogenous tissues of the body which 

 takes place during tke performance of its various functions; and 

 that urea was the form under which the metamorphosed or worn- 

 out nitrogenous tissues were chiefly eliminated from the system. 



2nd. That when an excess of nitrogenous matter was supplied 

 in the food, more than was suflScient to repair the waste of tissue, 

 that excess had the effect of producing a more rapid formation and 

 subsequent breaking up of tissue, and consequently increasing the 

 amount of urea eliminated in a given time ; but that , the increased 

 quantity of urea occurring in the urinary secretion was not due to 



