Heat-production Associated with Muscular Work. 105 



only slightly changed, so that the mean temperature of the gut is much the 

 same as that of the arterial blood entering it or of the venous blood leaving 

 it. The mixed blood that is sent from the heart, however, may simply, and 

 for the moment, be thought of as blood from the cooling district of the skin 

 plus blood from the warm district of the musculature, and, whereas the 

 blood from the skin may fairly represent the temperature of the mass that it 

 traverses there, it is not at once obvious that the blood returning from the 

 great bulk of the skeletal musculature, although of a quantity sufficient to 

 cope with the demands of a greatly increased oxygen-transport, should at 

 the same time be so increased as to keep the musculature at a temperature 

 only slightly greater than its own. The rectal temperature may conceivably 

 fail under such circumstances as an index of the average temperature 

 because the muscles are not represented in their proper proportionate value. 

 However, these are the difficulties of dealing with the events of the first 

 hour of cycling, and I propose to leave them on one side for the present, 

 until in a more extended form of publication I can deal with the details of 

 corrections for the temperature of the calorimeter and of the other measure- 

 ments which add to form this picture. We shall therefore pass at once to a 

 consideration of the events of the second hour. 



The Second Hour of Cycling. 



In each of the experiments represented by the data given subsequently 

 the subject entered the calorimeter, and having been sealed in, remained 

 seated until the balance of the surface of the calorimeter was well under 

 control. He was then signalled to seat himself on the cycle, and at a second 

 signal started to cycle at a fixed rate of 60 revolutions per minute. Outside 

 the calorimeter window an incandescent lamp was made to glow 60 times 

 a minute by the establishment of short-lasting contacts, one per second, by 

 a seconds-clock, and it was the cyclist's duty to keep pace. His performance 

 was watched by the cyclometer, and he was informed if the variations in his 

 pace were noticeable. As a general rule, however, the rate was excellently 

 maintained, and I owe many thanks to my long-suffering subjects, who 

 pedalled away in this monotonous fashion in each case for a period of 

 two hours. 



The values of the electrical brake were originally arranged so as to 

 separate the experiments into two groups. In one group the work done 

 upon the cycle was to be maintained at a value of 13 kalories per hour ; in 

 the second group at a greater value, 43 kalories. These values were obtain- 

 able by the maintenance of the 60-per-minute revolution rate in each case 

 and by sending in the one case a current of 1 ampere and in the other of 



VOL. lxxxvii. — b. I 



