830 NITROGENOUS METABOLISM. [BOOK 11. 



to be y grammes less than that of the ingesta ; in other words, that 

 y grammes of carbon have been stored up. Some carbon has been 

 stored up in the flesh with the nitrogen just considered ; this we 

 must deduct from y, and we shall then have y grammes of carbon 

 to account for. Now there are only two principal forms in which 

 carbon can be stored up in the body : as glycogen or as fat. The 

 former is even in most favourable cases inconsiderable, and we 

 therefore cannot err greatly if we consider the retention of y' 

 grammes carbon as indicating the laying on of b grammes fat. If 

 a + b are found equal to w, then the whole change in the economy 

 is known ; if w (a + b) leaves a residue c, we infer that in addition 

 to the laying on of flesh and fat some water has been retained 

 in the system. If w (a + b) gives a negative quantity, then water 

 must have been given off at the same time that flesh and fat were 

 laid on. In a similar way the nature of a loss of weight can be 

 ascertained, whether of flesh, or fat, or of water, and to what 

 extent of each. The careful comparison, the debtor and creditor 

 account of income and output, enables us, with the cautions 

 rendered necessary by the assumptions just now mentioned, to 

 infer the nature and extent of the bodily changes. The results 

 thus gained ought of course, if an account is kept of the water 

 taken in and given out, to agree with the amount of oxygen 

 consumed, and also to tally with the conclusions arrived at 

 concerning the retention or the reverse of water. 



Having thus studied the method and seen its weakness as well 

 as its strength, we may briefly review the results which have been 

 obtained by its means. 



522. Nitrogenous Metabolism. When a meal of lean meat, as 

 free as possible from fat, is given to a dog, which has previously 

 been deprived of food for some time, and whose body therefore is 

 greatly deficient in flesh, it might be expected that the larger part 

 of the food would be at once stored up to supply pressing 

 deficiencies, and that only the smaller part would be immediately 

 worked off as urea corresponding to the nitrogenous metabolism 

 going on in the body at the time, increased somewhat by the 

 labour thrown on the economy by the very presence of the 

 food. This however is not the case so far as the nitrogen of the 

 meal is concerned ; the urea given off is at once increased to such 

 an extent as to shew that an amount of the nitrogenous material 

 of the body corresponding to the greater part of the nitrogen of 

 the meal has undergone metabolism at once ; if this amount be 

 deducted from the total nitrogen of the meal the amount which 

 remains as an addition to the nitrogenous capital of the body is 

 comparatively small. At the next meal even this small quantity 

 is further reduced, the nitrogenous metabolism being still further 

 increased. If the diet be continued, and we are supposing the 

 meals given to be large ones, the proportion of the nitrogen which 

 is given off in the form of urea goes on increasing until at last 



