574 



plying lever be employed. It will usually suffice to weigh to ^ or 1 oz. 

 The weight of the body will be influenced by the quantity of food 

 taken, and by all the circumstances already noted in reference to the 

 emission of urine. Hence the body is heaver at night than in the 

 morning, also after a day of rest than after labour, in warm than in 

 cold weather, and in all conditions in which the bulk of the body is 

 increased, and the elimination of fluid lessened. There is a close 

 relation between sudden changes in the quantity of urine evolved and 

 the weight of the body. Among the excretions which cause a vari- 

 ation in the weight of the body, the carbonic acid, although a gas, 

 must not be overlooked ; and so far the weight will vary as the con- 

 ditions above mentioned vary the production of carbonic acid. Hence, 

 upon the whole, the determination of the weight at night is attended 

 by greater liability to error than in the morning, and the latter period 

 would alone suffice for the inquiry. A variation in the weight occurs 

 almost daily, and under some circumstances it amounts to from 1 to 

 2 Ibs. The varying weight of the body represents the varying quan- 

 tity of the fluid and solid excretions, the fat and the fluids in the 

 blood-vessels and tissues, besides the nitrogenous elements of the 

 body. Under the discipline of a prison, there is the highest propor- 

 tion of nitrogenous tissues to the weight of the body. 



FOOD*. 



The effect of food upon the system may be sought in two ways : 

 1st, the general effect of the ordinary dietary, which will represent the 

 actual condition of the body in the individual or in the masses, but 

 not the separate influence of any food. This is of great importance 

 when considered in relation to the community, and may show its actual 

 state under ordinary conditions. For this purpose the methods of 

 inquiry already referred to under the different subjects will suffice. 

 2nd, the effect of separate articles of food only. This can only 

 be ascertained in the absence of every agent acting upon the system, 

 except the one in question. Hence the food must be taken alone, 

 and before any other food has been eaten on that day, viz. before 

 breakfast. The inquiry must also be made with precisely a uniform 

 degree of exertion, and therefore at rest only, and in the absence of 

 all excitement and meteorological changes. If an unusual kind or 

 * See Phil. Trans. 1859. 



