1883.] Bodily Labour upon the Discharge of Nitrogen. 



13 



It will be obvious from the consideration of the experiments above 

 mentioned, that in approaching this qnestion, methods of research are 

 of prime importance. These divide themselves very naturally under 

 two heads — first, the diet, and secondly, the investigation of the 

 excreta in order that the results may be satisfactory. It is essential 

 first that the daily intake of nitrogen should be accurately known and 

 admit of exact regulation, and secondly that the mode of analysis of 

 the excreta should not be open to question. 



The use of the method of combustion with soda-lime effectually 

 disposes of the latter difficulty ; the former is not so readily over- 

 come. 



It is a matter of common knowledge that the composition of the 

 ordinary food-stuffs in their usual state is, from the chemist's point of 

 view, exceedingly variable. The first consideration then is how to 

 reduce them to such a state that this objection shall disappear. 



The mode in which I have overcome this difficulty constitutes the 

 chief difference between my experiments and those of other observers. 



It would occupy too much space, and is indeed unnecessary, to 

 describe in detail the process of preparation of the food-stuffs, and it 

 will here suffice to say that I have acted on the principle that only 

 fluids or powders can be accurately sampled and analysed ; all my 

 food-stuffs have been reduced to one of these states, and I may here 

 enumerate them — 



Meat (dried and ground to powder). 

 Flour. 



Vegetables (dried). 



Potato (Edward's patent desiccated). 



Condensed, milk. 



All these articles can be obtained in -quantity; all admit of being 

 easily and accurately weighed and measured ; they are in a state 

 which readily admits of accurate analysis, and will keep indefinitely. 

 Further they are the constituents of an ordinary mixed diet, and 

 except in their palatability and mode of preparation, involve no 

 serious departure from one's usual food. 



By the use of these materials T can, knowing their composition, 

 adjust the intake of nitrogen with the greatest possible nicety, and 

 maintain it at any desired level for almost any length of time, besides 

 having it in my power to use, not merely a similar, but precisely the 

 same, diet at any time when it may -seem desirable to repeat an experi- 

 ment. 



My plan of experiment was as follows : — 



Believing as I do that previous food may materially affect the 

 results of an experiment, and that the body has the power of storing 

 nitrogen at one time which can be discharged at another as occasion 



