ET) 
_XII.—The Effect of changing the Daily Routine on the Diurnal Rhythm in Body 
Temperature. By Sutherland Simpson, M.D., D.Sc. (From the Physiological 
Laboratory, Medical College, Cornell University, Ithaca, N.Y., U.S.A.) (With 
Thirteen Figures in the Text.) 
(MS. received November 20, 1911. Read January 8, 1912. Issued separately April 4, 1912.) 
CONTENTS. 
PAGE 
% INTRODUCTION . : ; : : ; : ; F : . 231 
ous WoRK ON THE Sean ; . ; ; ; : - ; , » 232 
a PRESENT INVESTIGATION k ; 5 5 : 3 é : F ; . 236 
IV. Resutts anp Discussion ; F : : ; . 246 
. Errect or Muscunar REst AnD Rerinre ON Bope Tinisacnne ns : 250 
_ Toe Retative VaLuEs or REcoRDS FRoM ReEctuM, MourH, aNp AXILLA, AS INDICATING Cainens 
In Bopy TEMPERATURE ‘ . ; ; j : ; : : . 257 
VI. Summary : ‘ ‘ . { : : , Ah : : 5 . 260 
I. InrRopvucrion. 
It is a well-established fact that the temperature of the human body is not con- 
stant, but shows a distinct and fairly regular daily rhythm. In the classical curves of 
JURGENSEN and LInBERMEISTER * the minimum is reached in the early morning, some time 
between the hours of 2 and 6, and the maximum in the late afternoon or evening, 
veen 4 and 8. In both there is a sharp morning rise, followed by a slight fall in 
late forenoon or early afternoon, and again a further rise to the maximum, which 
is reached some time between the hours stated. It has been demonstrated repeatedly 
many subsequent observers that this general type of curve is a more or less correct 
esentation of the changes which the rectal temperature undergoes, in the course 
he twenty-four hours, in a healthy individual leading an active life during the day 
id sleeping at night. 
While the presence of this daily rhythm is well recognised, the causes underlying 
are not clearly understood. The factors which are believed to affect the body 
mperature in health are muscular exercise, mental effort, ingestion of food, light, 
mperature of the surrounding medium, and sleep. Of these the first is the most 
portant. ach and all of these influences are active in the body at different periods 
ughout the twenty-four hours, but the exact relationship existing between them 
and the diurnal rhythm in the body temperature has never yet been satisfactorily 
demonstrated. 
By many it is held that the combined action of the several influences enumerated 
* JURGENSEN and LinBerMEIsTER, Handbuch der Pathologie und Therapie des Frebers, Leipzig, 1875. 
TRANS. ROY. SOC. EDIN., VOL. XLVIII. PART IT. (NO. 12). 36 
