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Effects of External Conditions 
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of 1907-1908 and 1908-1909. These curves are based upon 
Fig. 1 Chart showing temperature conditions in warm and cold rooms during experiments 
The continuous lines represent the temperatures for the 
as computed from four daily readings at equal intervals. 
the mean temperatures for each day, 
(1) mean date of birth of 
h the 2}$-month and 3-month meas- 
The heavy vertical lines (continuous and broken) denote 
earlier winter’s experiments, the broken lines those for the later year. 
each year’s mice; (2) mean date at which the 42-day measurements were made in each year; mean date at whic 
y ; 4 y year; (3 
urements were made. 
115 
