VALUE OF DIFFERENT MATERIALS OF FOOD. 245 



when an animal is undergoing starvation, is that which is occasioned by 

 the heat-producing process ; this, so long as the supply lasts, is kept up 

 by the store of fat, which is gradually consumed ; and when it is com- 

 pletely exhausted the temperature falls, hour by hour, until life can no 

 longer be sustained ( 117). The use of this store of fat, in supplying 

 any temporary deficiency in the food, becomes evident from such expe- 

 riments ; for when it has been completely exhausted, the withholding of 

 a single meal proves fatal, from the want of power to sustain the calori- 

 fying process. We find that animals, which are likely to suffer from 

 deficiency of food in the winter, or which spend that period in a state 

 of quiescence, have a tendency to accumulate a store of fat in the 

 autumn ; which tendency seems principally to depend upon the nature 

 of their food. We observe it chiefly in those Birds and Mammals which 

 live upon seeds and grains ; and these, when ripe, contain a large quan- 

 tity of oily matter, which thus becomes a valuable store against the time 

 of need. There are many birds, such as the beccafico, so much esteemed 

 in Italy, which are described, if killed at this season, as being " lumps 

 of fat." 



425. It is well known to breeders of cattle that some varieties or 

 breeds have a much greater tendency to the production of Adipose tis- 

 sue than others placed under the same circumstances ; and the former 

 are therefore selected to undergo the fattening process. Corresponding 

 differences may be met with among different individuals of the Human 

 race ; some persons having a remarkable tendency to the production of 

 fat, under circumstances which do not seem by any means favourable to 

 it, whilst others appear as much indisposed to this deposit. The latter 

 condition we notice particularly in that temperament which is commonly 

 termed the "bilious;" and it. is important to bear in mind that, where 

 such an indisposition exists, any superfluity of fatty matter in the food 

 taken into the system, must be excreted again through the liver, instead 

 of being retained and stored up in the body. It is very desirable, 

 therefore, that such persons should abstain from any excess of this kind ; 

 since an habitual call upon the liver, to relieve the system of a super- 

 fluity of fatty matter, is certain to produce a disordered state of that 

 organ ; and in order to prevent it, the diet should be altered, so as to 

 include less of fatty matter, or the amount of exercise should be in- 

 creased, so that it may be burned off by the additional respiration which 

 then takes place. 



426. We see, then, that the amount of food which can be properly 

 appropriated by the system varies considerably in different individuals, 

 and in the same individual under different circumstances. Consequently 

 it is impossible to give any general rule, which shall apply to every one 

 alike. The average quantity required by adult men, leading an active 

 life, and exposed to the ordinary vicissitudes of temperature in our own 

 climate, seems to be from 30 to 36 ounces of dry aliment. ^ But a 

 healthy condition may be kept up on scarcely more than half this allow- 

 ance, if the muscular powers are but little exerted, and the surrounding 

 temperature be high ; provided that it consists of substances of a nutri- 

 tious kind, united in proper proportions. 



427. The value of different substances as aliment depends in the nrst 



