30 
ON THE FOOD OF MAN IN DELATION TO HIS USEFUL WORK. 
Numerous other applications have been made of it, and its uses will increase as its 
wonderful properties become known .—American Journal of Pharmacy , March, 1865. 
ON THE FOOD OF MAN IN RELATION TO HIS USEFUL WORK. 
BY DR. LYON PLAYFAIR, C.B., F.R.S. 
Delivered at the Royal Institution , Friday , April 28, 1865.* 
This discourse was in three divisions. The first division treated of the amount of food 
required for mere subsistence ; then for the full health of the non-labouring adult; and 
lastly, of the quantity necessary for an active labourer. The second division of the dis¬ 
course discussed the question whether there was sufficient potential energy in the nitro¬ 
genous tissues, and in the oxygen required for their transformation, to account for the 
dynamical actions within or without the body. The question as to whether the fatty 
and amylaceous ingredients of the food co-operated in this work was brought under re¬ 
view. The third division of the discourse treated of the secretions per vesicam and per 
anum as measures of work. 
In the first division of *the discourse, a number of subsistence and low dietaries were 
recorded, and, as a general average, the following diets were given in ounces of 437£ 
grains:— 
Subsistence Diet in 
diet, oz. quietude, oz. 
Flesh-formers.2D 2-5 
Fat.0-5 1-0 
Starch, etc.12 0 12‘0 
Starch equivalent of heat given . . . 13‘2 14*4 
Carbon in food.6'7 7'4 
The speaker then examined the food of soldiers during peace as giving a fair average 
of food required by adult men, of soldiers engaged in work like the Royal Engineers, 
and of those exposed to the fatigues of war, as giving diets necessary for labourers. The 
following averages were given in ounces:— 
Flesh-formers 
Fat. 
Starch, etc. . . 
Starch equivalent 
Total carbon . . 
Soldiers 
during peace. 
. . 4-2 
. . 1-4 
. . 18-7 
22-4 
11-6 
Royal 
Engineers. 
5*1 
2-9 
22-2 
29-4 
14-8 
Soldiers 
during war. 
5-4 
2-4 
17-9 
23*5 
12-7 
Active 
labourers. 
5-6 
2-3 
20-4 
25-9 
13-9 
Active labour was defined to consist of work which would enable a man to walk twenty 
miles every day throughout the year, except on Sundays. The labour during war is 
much the same, for soldiers marching fourteen miles daily, with 60 lb. weight of ac¬ 
coutrements, exercise labour amounting to 776,160 foot-pounds, while the pedestrian 
walking twenty miles exerts a force of 792,000 foot-pounds. 
In the second division of the discourse, the speaker showed that the common experi¬ 
ence of mankind is in favour of the nitrogenous ingredients of food being the source of 
dynamical work. Horses and men, when labouring, are provided with food rich in such 
substances, and their labour was shown by numerical data to be proportional to the 
amount of the former. Thus, the work of a horse, divided by the work of an ox, gives 
the ratio 1: D43, while the plastic food of these animals, treated in the same way, 
yields 1: 1-44. In the same way, the work of a horse is eight times greater than that 
of a man, and the plastic food used for the external dynamical labour of each is nearly 
in the same proportion. The quotation of decomposition used by the author is the fol¬ 
lowing one:— 
Albumen. Urea or amido- Carbonic Water, 
carbonic acid. acid. 
_ C 24 H, 8 N 6 Q 16 + 100 O = 3 (C0 2 (N Ho) 2 ) + 21 C0 4 + 13 (H 2 0 2 ) 
w This discourse has since been published in extenso by Edmonston and Douglas, Edin¬ 
burgh. 
