412 PEACTICAL PHYSIOLOGY 



called constantine and copper make the most delicate junction. The 

 wires can be threaded down a fine gum-elastic catheter, and the 

 soldered end exposed in the eye of the catheter. The catheter can 

 then be passed up the femoral artery into the aorta. A similar thermo- 

 electric junction is buried in the substance of the organ under investi- 

 gation. The two junctions are put in circuit with a very sensitive low 

 resistance galvanometer. The needle of the galvanometer is provided 

 with a mirror. The instrument can be calibrated by placing two 

 junctions in water baths of different temperatures, and noting the swing 

 of the galvanometer on the scale. The temperature of the water 

 baths is determined by a delicate mercurial thermometer. 



For the investigation of frog's muscle Blix' apparatus is convenient. 

 The muscles are clamped above and fastened to recording levers 

 below. They lie in contact with constantine-copper junctions, which 

 are connected with the galvanometer. The galvanometer, junctions, 

 etc., make one compact piece of apparatus. The muscles are 

 enclosed by a cylinder of felt to prevent loss of heat. The 

 muscle on one side is excited, and the swing of the galvanometer 

 measured on the scale. At the same time the work done by the 

 muscle can be measured. Under the most favourable conditions, a 

 quarter of the energy of the muscle appears as work and three-quarters 

 as heat. 



The Loss of Heat in Man (Waller's Method). With the flat-bulbed 

 surface thermometer determine the surface temperature of the body at 

 various parts, e.g. the upper arm, thigh, face, abdomen. The deep 

 temperature of these parts 1 is also determined, and the temperature of 

 the air. The evaporation from the skin is determined by a hygro- 

 meter. This consists of a capsule containing calcium chloride. The 

 capsule is weighed and then applied to the skin. After 10 minutes 

 it is weighed again. The increase in weight gives the amount of 

 sweat evaporated. The operation is repeated at different parts of the 

 body. The area covered by the capsule is known. The total area of 

 the skin of the body can be calculated. The surface of an animal 

 is roughly proportional to ~1j of its volume. S = k JJv. The value of the 

 constant k is 11*2 for mammals (Riibner). Assuming the sp. gr. does 

 not vary in different animals weight can be substituted for volume in 

 this formula. Thus =11-2 jj weight of body. Thus the total loss 

 of water (and of heat) by evaporation can be calculated. The rate of 

 loss of heat from the skin can be inferred if the temperature 

 indicated by the surface thermometer be found when the instrument is 

 applied to a vessel of warm water which is losing heat at a known rate. 

 1 Axilla, groin, mouth, rectum. 



