INCOME AND EXPENDITURE OF BODY. 67 



tirium. There may, however, be at the same time an increase Of weight 

 which is due to the putting on of fat. If this is the case it must be ap- 

 parent that the protoplasm of the tissues is able to form fat out of proteid 

 material and to split it up into urea and fat. If fat be given in small 

 quantities with the meat, for a time the carbon of the egesta and in- 

 gesta are equal, but if the fat be increased beyond a certain point the 

 body weight increases from a deposition of fat; not, however, by a 

 mere mechanical deposition or nitration from the blood, but by an actual 

 act of secretion by the protoplasm whereby the fat globules are stored 

 up within itself. In a similar manner as regards carbo-hydrates, if they 

 are in small quantity, the whole of the carbon appears in the excreta, but 

 beyond a certain amount a considerable portion of it is retained in fat, 

 having been by the protoplasm stored up within itself in that material. 

 The amount of proteid material required to produce nitrogenous equi- 

 librium is considerable, but it may be materially diminished by the addition 

 of carbo-hydrate or fatty food or of gelatine to the exclusively meat diet. 



It is of much interest to consider how the protoplasm aots in convert- 

 ing food into energy and decomposition products, since the substance 

 itself does not undergo much change in the process except a slight amount 

 of wear and tear. We may assume that it is the property of protoplasm 

 to separate from the blood the materials which maj be required to pro- 

 duce secretions, in the case of the protoplasm of secreting glands, or to 

 evolve heat and energy, as in the case of the protoplasm of muscle. The 

 substances are very possibly different for each process, and the decomposi- 

 tion products, too, may be different in quality or quantity. Proteid ma- 

 terials appear to be specially needed, as is shown by the invariable pres- 

 ence of urea in the urine even during starvation; and as in the latter case, 

 there has been no food from which these materials could have been derived, 

 the urea is considered to be derived from the disintegration of the nitrog- 

 enous tissues themselves. The removal of all fat from the body in a star- 

 vation period, as the first apparent change, would lead to the supposition 

 that fat is also a specially necessary pabulum for the production of proto- 

 plasmic energy; and the fact that, as mentioned above, with a diet of 

 I lean meat an enormous amount appears to be required, suggests that in that 

 case protoplasm obtains the fat it needs from the proteid food, which pro- 

 cess must be evidently a source of much waste of nitrogen. The idea 

 that proteid food has two destinations in the economy, viz., to form organ 

 or tissue proteid which builds up organs and tissues, and circulating pro- 

 teid, from which the organs and tissues derive the materials of their secre- 

 tions or for producing their energy, is a convenient one, as it is unlikely 

 that protoplasm would go to the expense of construction simply for the 

 sake of immediate destruction. 



