76 DR SUTHERLAND SIMPSON AND DR J. J. GALBRAITH ON 



and XXXI.) had come to the laboratory from the same source. They were particularly 

 tame and very suitable for our purpose. They remained in the laboratory two or three 

 months after our observations had been made, during which time they gained rather than 

 lost weight, which is strong presumptive evidence that they were not tuberculous, but 

 when they were afterwards used for another purpose no post-mortem examination of the 

 internal organs was made, and so it could not be definitely stated that these animals 

 were free from tuberculous disease and that the curves obtained were from normal 

 animals. These curves, however, were found to be exactly similar to those got during 

 our later investigations from monkeys who were undoubtedly free from tuberculous 

 disease, so that they may be fairly claimed as normal curves. 



PART II. 



Introduction. 



We then resolved to make a more extended series of observations with the view of 

 investigating more accurately the character and amplitude of the normal wave and 

 ascertaining the factors which determine its occurrence. The commonly assigned 

 causes of the normal fluctuations of body temperature are : — muscular exercise, sleep, 

 ingestion of food, inanition, light, and the temperature of the surrounding medium. 

 The exact relationship between these various influences and the diurnal temperature 

 variation has never been satisfactorily demonstrated, the relative importance of the 

 factors has not been estimated, nor has it ever been conclusively shown that the varia- 

 tion depends upon these various factors. Carter (5) and others have found that the 

 curves of heat production and heat loss do not coincide with the temperature curve. 

 If this diurnal wave be due to the combined action of the various factors enumerated 

 above, then it might be expected that any modification of them would produce a 

 change in the form of the curve, or, in the simplest and most complete case, total 

 inversion of the daily routine would cause a corresponding change in the curve. This 

 had already been tried in man by several observers, but the conclusions arrived at are 

 contradictory. However, in the most recent and at the same time most carefully 

 planned and executed experiments on this question, carried out by Benedict (6), this 

 observer was unable to produce an inversion of the temperature curve by inverting the 

 daily routine of life. This would tend to show that either the temperature wave was 

 not caused by the alternation of rest and activity, or that the control or co-ordination of 

 the causal factors was sufficiently perfect to maintain a practically constant temperature 

 with no discoverable inversion of the swing, or that there existed a habit of tempera- 

 ture variation, whatever the actual causal factors of the variation be, too powerful to be 

 eliminated during the course of a short series of observations. 



As noted above, our previous observations had shown that in the monkey, after 

 every precaution against fallacy had been taken, there existed a wave of an amplitude 





