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



of these it was greatest in D, a very old specimen, and not, as one would have expected, 

 in C, which was immature. In the curve compounded from the mean of all five 

 monkeys (fig. 6, p. 88), the minimal point is reached at 5 a.m., the maximal at 

 5 p.m., and the range is 1*62° (37*25 to 38*87). In this compounded curve the 

 rise is most rapid from 7 to 9 a.m. ; from 9 a.m. till 5 p.m. it is very regular, 

 but slower ; from 7 p.m. to 1 a.m. the fall is most rapid ; it is very slow between 

 1 a.m. and 5 a.m., after which it again begins to rise. There are no secondary 

 curves. In monkey B # (red curve in chart L), the range for the whole period was 

 2'G° (36*7 at 3 a.m. April 11th to 39'3 at 5 p.m. April 8th), in C (blue) 2'9° 

 (367 at 3 a.m. on April 9th to 39'6 at 7 p.m. on April 7th), in D (green) 3-4° 

 (35*8 at 7 a.m. April 6th to 39*2 at 5 p.m. April 5th), in E (not represented in 

 chart I.) 27° (36 '5 at 3 a.m. April 7th to 39 "2 at 7 p.m. April 4th), in F (not in 

 chart I.) 2*3° (36 - 8 at 5 a.m. April 4th to 39 "1 at 7 p.m. April 5th), and in the mean 

 of all five 2° (37'0 at 3 and 5 a.m. April 9th to 39 "0 at 3 and 5 p.m. April 8th). The 

 greatest range in any single period of twenty-four hours was in B (red) 2 "4° (36*7 at 

 3 a.m. April 11th to 39*1 at 7 p.m. April 10th), in C (blue) 2'6° (367 at 3 a.m. April 

 9th to 39-3 at 5 p.m. April 8th), in D (green) 3'4° (35-8 at 7 a.m. April 6th to 39"2 at 

 5 p.m. April 5th), in E 2-5° (367 at 3 a.m. April 5th to 392 at 7 p.m. April 4th), in 

 F 2-0° (36 - 8 at 5 a.m April 4th to 38'8 at 5 p.m. April 3rd), and in the mean of all 

 five 2° (37-0 at 3 and 5 a.m. April 9th to 39 '0 at 3 and 5 p.m. April 8th). 



PERIOD II. 



This extended from 5 p.m. on April 12th till 5 p.m. April 20th. During this 

 period the conditions were completely reversed ; the resting period was now from 9 a.m. 

 to 9 p.m., and the active period from 9 p.m. to 9 a.m. The monkeys were tied up at 

 9 a.m., the room darkened and silence ensured; at 9 p.m. they were set free, and at 

 the same time the room was brightly illuminated by a powerful electric light. During 

 the active period under the reversed conditions much of the observers' time was spent 

 with them, but beyond this no artificial means were employed to make them adopt 

 the new routine. They were now fed at 6 a.m. and 9 p.m. They were not allowed 

 to rest on the night preceding this period, so that they might sleep during the 

 succeeding day, and no temperature readings were taken from 7 p.m. April 11th till 

 5 p.m. April 12th. 



The result was a complete reversal of the diurnal variation curves, as may be seen 

 in figs. 1-6, t pp. 86-88, and in chart I. By the third day the rhythm is Avell 

 established, and it is maintained to the end of the period, while the regularity of the 

 curves compares favourably with that of Period I. 



* See p. 77 for description of this and other monkeys, C, D, E, F. 



t The diurnal curve for this period is represented by the interrupted line. 



