SUBSISTENCE AND OTHER DIETS. 921 



carbonic acid is, here also, as 1 to '7. Urea itself is regarded* as a compound 

 of carbonic oxide and ammonia, and its carbon, as being only partially oxi- 

 dized. Of the hydrogen, three-fourths are deducted, as being either already 

 combined with oxygen, or as belonging to the ammonia. The heat-units are 

 accordingly calculated for so much carbonic acid, carbonic oxide, and water, 

 and also for sulphuric acid formed by the sulphur of the albumen. One ounce 

 of albumen, 437.5 grains, or 28.35 grammes, if thus decomposed, would yield 

 126,500 heat-units, the mechanical equivalent of which is 53,762 met. kils. 

 Hence the 2 oz. of flesh-formers in the subsistence diet, would afford 107,524 

 met. kils. of work, which exceeds the essential vital work performed in the 

 body in the condition of convalescence, the work of the heart representing the 

 largest item of the internal mechanical or vital work, being taken at 37,781 

 met. kils., which, however, is too small an estimate. Again, the 3 oz. of 

 additional albuminoid food consumed by the active laborer, are mechanically 

 equivalent to 188,167 met. kils. ; whilst the mean amount of laborious work is 

 only equal to 105,605 met. kils. Lastly, the 5^ oz. of albuminoid food con- 

 sumed by the active laborer, yield 295,691 met. kils. ; whereas his total me- 

 chanical work, external and internal, is, as we have seen, only 250,000 met. 

 kils. Even if each of the above-mentioned mechanical equivalents of the al- 

 buminoid food be reduced by one-twelfth, for that which passes off in the solid 

 excreta without undergoing combustive change, still, in each case, enough 

 power remains, derived from the oxidation of the albuminoid food, to execute 

 the mechanical work, whether internal or external, performed by the body. 



It is maintained by Playfair, that the blood cannot be the source of the 

 motor power, but this opinion is open to question. The quantity of fat in 

 muscular tissue, only 2 per cent., is too small to accomplish it. The fat in 

 the heart could only yield 10,157 met. kils., whilst the work of the heart is 

 estimated as equal, at least, to 37,780 met. kils. In 4 oz. of dried flesh, there 

 would be 150 grains of fat, which would yield 36,888 met. kils., whilst that 

 amount of muscular substance itself would yield 214,544 met. kils. The fat 

 of muscle being therefore wholly inadequate to produce the mechanical work, 

 it is presumed, by Playfair, that the larger quantity yielded by the muscle 

 itself, must be regarded as its source. Moreover, the fatty substances, as we 

 know, are wanted for heat-giving purposes. They are required, we may add, 

 to supply the waste of the nervous substance in muscular action ; and the fat 

 in the muscles may protect them from oxidation, when no movement is taking 

 place ; but fat alone cannot act vicariously as a substitute for albuminoid 

 food. In starving animals, the fat wastes gradually day by day, undergoing 

 oxidation at an equal daily rate, whilst the muscle wastes irregularly, at 

 first slowly, then more uniformly, but, at the approach of death, very slowly 

 indeed, the mechanical work, external and internal, being reduced to a mini- 

 mum. 



The amount of albumen allowed in the dietary of Vierordt (p. 901), after 

 deducting the urea, and T \,th for loss by the solid excreta, would yield 680,000 

 heat-units, or a mechanical equivalent of 264,152 met. kils., a quantity closely 

 corresponding with the amount obtained by Playfair's calculations, and like- 

 wise exceeding the estimated total daily mechanical work of 250,000 met. kils. 



The small balance of unemployed force is regarded by Playfair as proving 

 the extreme economy of the operations of the living body. If, indeed, the 

 mechanical work derived from the chemical energy developed in the oxidation 

 of 3 oz. of excess of albuminoid food, viz., 188,167 met. kils., be compared 

 with the external mechanical work of an actively employed laborer, 105,605 

 met. kils., the proportion of actual work to the total producible energy is about 

 as 1 to l. In comparing the total work performed, 250,000 met. kils., with 

 the total heat produced from all the food, 295,691 met. kils., more than ths of 

 the chemical energy developed are utilized, instead of 4,th, as estimated by 

 Helmholz, and others, and instead of ^th, as is the case in the best steam- 

 engines. Every particle of energy developed in the body is probably, in some 

 way, usefully employed. 



The researches of the Rev. Dr. Haughton on excreted products, 

 taken as the measure of work, bear on this question of the source of 



