FARMERS' INSTITUTES. 407 



aud nervous systems, while the carbohydrates maintain the animal heat, and 

 serve as a storehouse of force to sustain the working animal. The requirements 

 of an animal in regard to one or other class of food will depend upon its con- 

 dition ; if growing and forming muscular tissue, or if in milk, and thus part- 

 ing with albuminoids in the cheesy matter of milk, it will require a relatively 

 large amount of albuminoids ; if at work, it Avill require more of carbohydrates 

 as well as albuminoids. 



As all animal force is manifested through muscular contraction, it was sup- 

 posed that every contraction of the muscles must be attended by a correspond- 

 ing waste of the muscles, and as the albuminoids are directly concerned in 

 repairing the waste of the muscular system, it was supposed that the albumin- 

 oids emphatically represented the force-forming elements in food, and phys- 

 iologists formerly attempted to measure the labor-value of food by the amount 

 of albuminoids present, and the amount of work done by any animal by the 

 quantity of nitrogen excreted. It puzzled the physiologist to explain how labor- 

 ing men could perform so much work on fat pork, and especially, how they 

 could consume so much fat in mild weather, wlien no addition to the animal 

 heat was required, since they supposed that the only ofltice of fat was to develop 

 heat. Yet these workmen would live and labor in spite of the plainest laws of 

 physiology ! The explanation offered was that the laborer had become accus- 

 tomed to eat fat pork in cold weather when it was required to keep up the ani- 

 mal temperature, that from force of habit he continued to eat it in warm 

 weather when it was not needed, and that his strong constitution and open-air 

 life enabled him to violate the plainest laws of physiology without any imme- 

 diate disaster, but the fat could be of no service except to keep up the animal 

 heat. But the workman was wiser than his teacher, and instinct led him to 

 better conclusions than the dogmatic assertions of theoretical science. Within 

 a few years past very careful experiments have shown that work is not attended 

 by a corresponding waste of tlie muscular system, but is attended by a largely 

 increased consumption of carbohydrates, such as fat, sugar, and starch; that 

 there is a marked increase in the amount of carbonic acid thrown out of the 

 system, but no marked increase in the excretion of nitrogen in the form of 

 urea. The comparison is made of the muscular system to the steam engine, 

 and the carbohydrates to the fuel whose combustion generates the steam which 

 gives force in the engine ; a certain amount of force in the engine requires the 

 consumption of a definite amount of fuel ; if the engine is kept in good repair, 

 the amount of force which it can exert may be measured by the amount of 

 fuel it consumes ; just so the performance of a certain amount of work by an 

 animal requires the consumption of a certain amount of food — of albuminoids, 

 to keep the muscular engine in good repair, and of carbohydrates, to furnish 

 the force to run the enorine. 



o 



FOKCE-VALUE. 



Different kinds of fuel have marked difference in the amount of heat tliey 

 will produce when burned ; a hundred pounds of charcoal will make more 

 steam than a hundred pounds of dry wood, because even the driest wood is 

 made up of about equal parts of carbon, hydrogen, and oxygen, united in 

 proportions to form water, /. e., the wood is inade up of equal weights of car- 

 bon and water, chemically combined. The charcoal is made up almost entirely 

 of unburned material or carbon, while perfectly dry wood contains only half 

 its weight of unburned materials. We may say that the charcoal contains the 

 heat-forming material in a more condensed form than the wood. 



