150 LAWRENCE R. PROUTY AND JAMES D. HARDY 



The rectal thermometer consists of a silver tube 25 mm. long, 3 mm. 

 in diameter and 1 mm. in wall thickness. A small bead of Wood's 

 metal is dropped into the bottom of the silver tube and the thermo- 

 junction embedded within it. The leads from the thermocouple are 

 carried through small rubber tubing. The instrument is particularly 

 adapted for use in children and laboratory animals. Readings are 

 made directly from the galvanometer scale which is calibrated in de- 

 grees Centigrade. To make a reading, the thermometer is inserted 

 into the Thermos flask with the cold junction and the galvanometer 

 set to read the flask temperature. The thermometer is then re- 

 moved and inserted approximately two inches into the rectum. 

 Reliable readings can be obtained to ± 0.02°C. 



For smaller laboratory animals such as mice or guinea pigs, the 

 junction measuring rectal temperature is embedded in latex rather 

 than contained in a silver tube. This prevents rupturing the colon 

 and permits retention in the animal for periods as long as 48 hours 

 without damage to the rectal mucosa. Figure 6 shows the arrange- 

 ment for quickly measuring the temperature of as many as ten ani- 

 mals (7) . More elaborate rectal thermometers are available commer- 

 cially. These instruments are usually of the recording potentiometer 

 variety and have a precision of ±0.01°C. 



Blood and Tissue Temperatures. Recently, Bazett (8) and 

 co-workers have described a method for obtaining measurements of 

 arterial and venous blood temperature by inserting a catheter 

 containing a fine thermocouple into arteries and veins for consider- 

 able distances. This technique opens a new field for the measure- 

 ment of blood flow in various parts of the body and for investigating 

 more thoroughly the temperature-regulating functions of the hypo- 

 thalamus. Since these catheters can be inserted without undue 

 hazard to the subject, studies of the thermal exchanges in the larger 

 organs of the body can now be made under a wide variety of cir- 

 cumstances. 



Thermocouples inserted in long hypodermic needles are available 

 on the market for the measurement of intramuscular temperature. 

 More accurate measurements of intramuscular temperature can be 

 made by sewdng into the muscle fine wire thermocouples suitably pro- 

 tected with insulating varnish. In vivo studies of the heat of muscular 

 contraction in man and animals have been possible with these tech- 

 niques. Surprisingly wide variations in temperature have been dis- 



