776 
Bose. — On Diurnal Variation of 
due to excess of turgor, the latter attaining its maximum at about 7 a.m. 
And, lastly, we have the depressing effect of cold, the temperature minimum 
occurring at 4 a.m. On account of the combined effects of these various 
factors, and the phenomenon of lag, the period of minimum excitability is 
in general reached about 9 a.m. In certain other cases this may occur 
Fig. 16. The continuous curve shows the relation between the hour of the day and temperature. 
The dotted curve exhibits relation between the hour of the day and excitability. 
earlier. After the attainment of this minimum, the excitability is gradually 
and continuously increased, under the action of light and of rising tempera- 
ture. In the present case the highest temperature, 28° C., was reached 
at noon, and the maximum excitability attained an hour afterwards. 
It was said that temperature exerted a predominant influence in 
inducing variation of excitability. We may therefore expect that the 
diurnal period would be modified in a certain way according to the season. 
