256 DR SUTHERLAND SIMPSON ON 
From the preceding remarks will be seen the importance of making full allowance 
for the elements of muscular exercise particularly and of food im all investigations 
similar to that undertaken by the writer. The ideal experiment would be to eliminate 
muscular exercise and food entirely, but this, of course, cannot be done (except at 
comparatively long intervals) and the body still be maintained in perfect health. It is to 
be regretted that a similar resting and fasting experiment was not made in the control 
period before leaving Ithaca for Scotland, and again immediately on arriving in 
Edinburgh. Any inherent diurnal rhythm which might be present would not, under 
these conditions, be masked by external influences, but I think the proof is 
sufficiently clear that there is no such rhythm. When the external conditions were as 
nearly as possible the same in the three localities mentioned, viz. the Orkneys, 
Winnipeg, and Ithaca, the curves are practically identical in character, and there is no 
indication of a Scottish rhythm being carried in the body to Winnipeg. In each of 
these curves (figs. 7 and 8) there is a slight morning rise and evening fall. The 
former comes in the period between sleep and full wakefulness, and the latter 
appears when daylight is replaced by artificial light, which again induces a feeling of 
drowsiness. 
During natural sleep the temperature of the body falls markedly, and much more so 
in the deeper sleep induced by narcotic drugs such as morphine, alcohol, etc. This is 
due in part to a diminution in muscular tonus which leads to a lessened heat-production, 
and in part to the fact that sleep is accompanied by a cutaneous vaso-dilatation 
allowing of an increase in heat-loss. Any condition which diminishes the activity of 
the heat-regulating mechanism, situated somewhere in the central nervous system, will 
tend to induce a state of poikilothermism, and then the temperature will fall if the 
temperature of the environment is lower (as it almost always is in temperate climates) 
than that of the body. Any tendency to somnolence, therefore, will be marked by 
some fall in the body temperature. 
If the curves of August 8 (Orkney) and August 29 (Winnipeg) be compared 
(figs. 7 and 8), it will be seen that in the former both the morning rise and the evening 
fall are more distinct than in the latter. As explained previously, this is probably due 
to the fact that the subject was more quiescent on August 29. If the Scottish 
temperature rhythm had been carried in the body to Winnipeg, the morning rise and 
the evening fall should begin some six hours earlier; the former, therefore, would not 
come into the Winnipeg curve at all, and the rectal temperature would be already high 
when the first observation was made at 6 a.m., while the latter would begin about 
12 (noon) or 1 p.m. instead of 6 or 7 p.m. As a matter of fact, a slight fall is 
noticeable in the Winnipeg curve at 1 p.m., but this is succeeded by a rise later which 
should not be if this corresponded with the Scottish evening fall. These two curves 
are remarkably alike in every respect. There are minor differences, but these are not 
greater than one might expect to find in any two similar curves taken in the same 
locality on consecutive days. 
