Page:The Annual Register 1899.djvu/533

 1899.] SCIENCE. 109

Mr. Pembrey has taken a large number of temperature observations on healthy men. He finds that mental work has little or no effect, that food causes only a slight rise, but that a considerable increase of heat is caused by muscular exercise. Mr. Woodhead has obtained a similar result from experiments on the temperature of the horse after exer- tion.

M. Chauveau has endeavoured to ascertain the heating effects of exercise in three cases. In the first case a man, treadmill fashion, -works a friction wheel, the whole enclosed in a calorimeter. In the second case, the man remains inside the calorimeter, but the friction wheel is outside. In both cases the muscular action is that of walking upstairs. The third case resembles the second, except that the action is that of going downstairs. In addition, the evolution of water-vapour and carbon dioxide was measured in order to estimate the liberation of chemical energy. The results show that in doing " positive work " the bodily production of heat is 200 calories per hour, and in doing "nega- tive work,*' 170 calories per hour. It does not appear how a proper •supply of oxygen was maintained.

Dr. Foxwell points out that the first effect of exercise is an increase of the respiratory exchange, whilst the respiratory quotient, COj/O a , remains undiminished. This necessitates a large increase in the ab- sorption of oxygen during exertion, a man giving off ten times as much carbonic oxide when on the treadmill as he does when asleep. He -elicits the remarkable fact that arm-work, per unit of work done, requires a greater absorption of oxygen than leg-work. Thus, if the amount of oxygen absorbed during sleep be 100 grams per minute, then walking on the level it would be 500 grams, climbing a steep hill 5,000 grams, and while doing the same amount of work by turning a wheel with the arms, 7,000 grams. It should not, however, be overlooked that as the muscles of the arms are fixed to the thorax, their contractions produce a greater respiratory and cardiac disturbance than can be caused by leg-movement.

If a muscle, in a warm-blooded animal, be directly stimulated by the alternating electric current it can be thrown into 40 contractions per second. Their frequency in pathological tremors is from 9 to 12 per second, and as an effect of neural function about 10 per second. It appears therefore that it is the nervous structure and not the muscular that limits the rapidity of response. This neuro-muscular phase was dwelt upon last September at the Dover meeting of the British Asso- ciation by Professor Richet, who pointed out that the time-rate 01" held good generally for "la vibration nerveuse" Thus, the electric oscillations of the spinal cord are 8-10 per second, the retina cannot receive more than 10-11 distinct sensations in a second, sound undula- tions when they exceed 8 per second are perceived not separately but as a continuous musical note, it is impossible to articulate distinctly more than 10 syllables per second, and they cannot be mentally repro- duced at a more rapid rate.

This value then, 0*1", being the psychological unit of time, the minimal duration which is appreciable by human intelligence, the high frequency of sound waves and the prodigiously rapid undulations of