Enquiry into the Heat given out by the Human Body. 253 



Therefore out of nineteen experiments only three show a fall in 

 the amount of heat emitted after lunch. Of these three, one (W. M.) 

 is easily accounted for from the digestion of the person under 

 experiment being on that day somewhat out of order, and very 

 little food being taken. In the other instances, in which the labo- 

 ratory boy was in the calorimeter, he acknowledged finding it diffi- 

 cult to sit quiet, and movement may easily account for the irregular 

 result. 



It follows from these experiments that the rule is an increase in 

 the emission of heat from the body after a full meal. 



Finally it was of interest to ascertain how far the heat emitted by 

 the body is in proportion to the weight of the body. The following 

 table shows clearly that this relation is subject to great variations ; 

 the lightest person under experiment, also the youngest (being 

 sixteen years of age), gave out a mean amount of heat per kilo, 

 weight greatly exceeding all the others. 



When the work connected with this paper was nearly completed, 

 it occurred to us that there were two important omissions in the 

 enquiry. The first was the neglect to take into account the heat lost 

 from the calorimeter by the air expired when it was collected for 

 analysis ; * on the other occasions the air was expired into the calo- 

 rimeter, and therefore there was no loss of heat from that cause. 

 We now made a few experiments, taking the temperature of the air 

 expired at its exit from the chamber. The excess of this tempera- 

 ture over that of the air inspired was used for calculating the heat 

 lost, and the correction introduced where necessary. This figure 

 varied somewhat for each person under experiment. The second 

 omission was leaving the carbonic acid which might have collected 



* Supposing the air expired was found on its exit from the calorimeter to be 

 8 C. higher than the external air, and that this volume of air reduced amounted 

 to 112'5 litres in 25 minutes, this would give a weight of 145'5 grams of air, 

 which multiplied by the specific heat of air (0'2375) and by 8, the excess tem- 

 perature = 276-4 calories, or for an hour 663 calories. On a total heat of 95,000 

 calories, the heat thus lost would only amount to 0'7 per cent. 



