410 PEACTICAL PHYSIOLOGY 



decreased, but the blood is more watery. In pernicious anaemia, on 

 the other hand, the total amount of haemoglobin is diminished. 



Ventilation. The ventilation per hour of a room may be determined 

 by burning one or more candles in it and estimating with Haldane's 

 gas analysis apparatus the percentage of C0 2 in the air of the . room. 

 The amount of C0 2 produced per hour by the candle must be deter- 

 mined beforehand. To determine this the candle may be placed in 

 a large air-tight bottle, through which a current of air is aspirated. 

 The air is analysed by the Haldane-Pembrey apparatus. The air in a 

 room of 1000 cubic feet is changed at least once an hour even when 

 the doors and windows are shut. The ventilation takes place through 

 the walls. The wall area in proportion to the cubic content of a 

 room varies inversely as the square of the diameter. Thus the larger 

 the room, the worse is the ventilation. 



CHAPTER XL VIII. 

 PRODUCTION AND LOSS OF HEAT. 



Methods of Investigating the Seats of Heat Production. The 



temperature of the organs of the body can be investigated by either 

 delicate thermometers calibrated in T J-<jth of a degree between 35 and 

 40 C., or by thermo-electric junctions. 



The thermometers are made with long slender bulbs. One is passed 

 up the femoral artery into the blood stream of the aorta. The other is 

 used to measure the temperature of the organ during states of rest and 

 activity. 



(1) In the case of the salivary gland a j_-tube is connected with the 

 duct-cannula and with a reservoir full of warm water. The ther- 

 mometer is inserted in one branch of the -tube, and the latter is filled 

 with the warm water. When the temperature of the water has 

 reached the same level as the aorta, the chorda tympani is stimulated. 

 The saliva is found to be not perceptibly hotter than the aortic 

 blood (Hill and Bayliss). The circulating blood carries away the small 

 amount of heat formed in the gland. Eeid failed to demonstrate heat- 

 production in the liver on stimulating the hepatic nerves. 



(2) In the case of the muscles a thermometer is buried in the thigh 

 muscles of each leg. The circulation is then temporarily arrested by 

 compression of the aorta and the sciatic nerve excited on one side. 

 The tetanised muscles show an increase in temperature. 



