528 A MANUAL OF PHYSIOLOGY 



Or (c) a large number of sweet oranges may be eaten. 



If experiments (a), (b) and (c) are all unsuccessful, (a) and (b) may 

 be repeated on a dog. 



3. Measurement of the Quantity of Heat given off in Respiration. 

 This may be done approximately as follows : Put in the inner copper 

 vessel, A, of the respiration calorimeter (Fig. 140, p. 493) a measured 

 quantity of water sufficient to completely cover the series of brass 

 discs. Place A in the wider outer cylinder, the bottom of which it 

 is prevented from touching by pieces of cork. The outer cylinder 

 hinders loss of heat to the air. Suspend a thermometer in the water 

 through one of the holes in the lid. In the other hole place a glass 

 rod to serve as a stirrer. Read off the temperature of the water. Put 

 the glass tube connected with the apparatus in the mouth, and breathe 

 out through it as regularly and normally as possible, closing the 

 opening of the tube with the tongue after each expiration and 

 breathing in through the nose. Continue this for five to ten minutes, 

 taking care to stir the water frequently. Then read off the tem- 

 perature again. If W be the quantity of water in c.c., and / the 

 observed rise of temperature in degrees Centigrade, W/ equals the 

 quantity of heat, expressed in small calories (p. 493), given off by the 

 respiratory tract in the time of the experiment, on the assumptions 

 (i) that all the heat has been absorbed by the water, (2) that none 

 of it has been lost by radiation and conduction from the calorimeter 

 to the surrounding air. Calculate the loss in twenty-four hours on 

 this basis ; then repeat the experiment, breathing as rapidly and 

 deeply as possible, so as to increase the amount of ventilation. The 

 quantity of heat given off will be found to be increased.* 



In an experiment of short duration (2) is approximately fulfilled. 

 As to (i), it must be noted that in the first place the metal of the 

 calorimeter is heated as well as the water, and the water-equivalent of 

 the apparatus must be added to the weight of the water (p. 494). The 

 water-equivalent is determined by putting a definite weight of water at 

 air temperature T into the calorimeter, and then allowing a quantity 

 of hot water at known temperature T' to run into it, stirring well, and 

 noting the temperature of the water when it has ceased to rise. Call 

 this temperature T". Enough hot water should be added to raise 

 the temperature of the calorimeter about 2 C. The quantity run 

 in is obtained by weighing the calorimeter before and after the hot 

 water has been added. Suppose it is m. Let the mass of the cold 

 water in the calorimeter at first be M, and let M' = the mass of water 

 which would be raised 1 C. in temperature by a quantity of heat 

 sufficient to increase the temperature of all the metal, etc., of the calori- 

 meter by i in other words, the water-equivalent of the calorimeter. 



The mass m of hot water has lost heat to the amount of 

 m (T - T"), and this has gone to raise the temperature of a mass of 

 water M, and metal equivalent to a mass of water M', by (T" - T) 



* The average heat-loss by the lungs for 5 1 men (calculated for the 

 24 hours) was 312,000 small calories for normal, 919,00*0 for the fastest, 

 and 195,000 for the slowest breathing. 



