MECHANICAL WORK OF THE BODY. 917 



i. e., much above the average standard. The adoption of this number would 

 reduce the deficit to 300,000 heat-units, which would be provided for by a daily 

 addition of 37 grammes of carbon in the food, a quantity which would be con- 

 tained in 3 oz. of starch, or 1 oz. of fat. According to Playfair's Tables (p. 

 920), such an additional quantity is actually consumed. The results of im- 

 proved methods of research and calculation, therefore, quite support Lavoi- 

 sier's chemical theory of animal heat. 



Mechanical Work of the Body. 



The daily working power of a Man, and the actual mechanical work done, 

 according to his individual strength, must vary greatly according to the exer- 

 cise or labor he undergoes. It is said that a Man can raise 100 Ibs., 1 foot in 

 a second, for 8 or 10 hours in the day; that, on level ground, he can draw 640 

 Ibs. weight; that he can lift 286 Ibs. with both hands, and support on his 

 shoulders, 330 Ibs. The daily work of a Man is said to be between ith and ^th 

 of that of a horse. More exact computations show, that with severe labor, the 

 daily work of a man is equal to 207,871 met. kils., or 1,500,000 ft. Ibs. (Ranken); 

 with moderate labor, it is not more than 66,518 met. kils. , or 480,000 ft. Ibs. (Ran- 

 ken.) The work performed by pedestrians has been estimated at 109,570 met. 

 kils. , or 790,720 ft. Ibs. (Haughton). In marching, a soldier exercises a tractive 

 force equal to ^th of the weight of his body, arms, and accoutrements. The 

 coefficient of traction is, therefore, expressed as being ^th of the weight to be 

 moved; hence, a soldier weighing 150 Ibs., with 60 Ibs. of weight to carry, and 

 marching 14 miles per day, performs work equal to 107,560 met. kils., or 

 776,160 ft. Ibs. (Playfair). 



Thus 150 + 60 20 Ibs. x 14 x 5280 feet = 776,160 ft. Ibs. 



The mean of 9 estimates of laborious work, according to various authori- 

 ties, is 105,605 met. kils., or 762,048 ft. Ibs. This represents the daily external 

 mechanical work of the body. Of the internal mechanical work, a large por- 

 tion, which is usually referred to the external work, is that which poises the 

 body and supports it. Next to this, is the true internal work, of which the 

 most is performed by the heart, which has been estimated by one authoritj^ at 

 37,871 met. kils., or 273,280 ft. Ibs. (Haughton); and by another at 70, 000 met. 

 kils., or 492,520 ft. Ibs. in 24 hours; the daily work of the left ventricle alone, is 

 estimated at 46,000 metre-kilogrammes. (Vierordt.) Another estimate gives 

 43,000 met. kils. for the left ventricle, and 21,000 for the right ventricle, mak- 

 ing a total of 64,000. (Bonders.) According to the lowest estimate, the work 

 of the heart, which is always beating, is equal to more than d, and, according 

 to the highest, to nearly |ds of the total daily external work. Taking the high- 

 est estimate of the heart's work, and adding it to the mean labor-work of Man, 

 as above estimated, we arrive at the sum of about 175,600 met. kils. To this 

 must also be conjoined the work of respiration, i. e. of the diaphragm and the 

 intercostal muscles, 63,000 met. kils. (Bonders), the work of the digestive 

 organs, and other internal mechanical work, which will probably raise the 

 total daily mechanical work, external and internal, performed by a man en- 

 gaged in active employment, to the sum of 250,000 met. kils. From other 

 calculations, Vierordt adopts 200,000 met. kils., but exclusive, as it would 

 seem, of the internal work. Again, the actual mechanical effort, or work, 

 accomplished by a muscle, is equal to the product of the weight lifted, multi- 

 plied by the height to which it is lifted. Thus, with a frog's muscle, Weber 

 found that 5 grammes were lifted 27.6 millimetres, 15 grammes 25.1 mm., 25 

 grammes 11.45 mm., and 35 grammes 6.3 mm. The products of these num- 

 bers, showing the work accomplished in each case, are respectively 138, 376, 

 286, and 220 gramme-millimetres. Hence, although the work effected at first 

 increases with the load, it soon reaches a maximum, and then diminishes. 

 Since every muscle becomes exhausted by work, and requires intervals of rest 

 for reparation, it is necessary, in order to determine the actual mechanical 

 work accomplished by a man or animal, to take into account the element of 

 time. In this way, it has been estimated that the mechanical work of a Man 

 is represented by 7 met. kils. per second, and that of a horse, by from 60 to 70 



