Ill 
Moto-excitability in Mimosa. 
In winter the night temperature falls very low ; hence the depression of 
excitability is correspondingly great, and results in the complete abolition 
of excitability. The after-effect of intense cold is seen in the condition of 
inexcitability persisting for a very long period in the morning. In summer 
the prevailing high temperature modifies the diurnal periodicity in a different 
manner. When the night is warm, the fall of excitability is slight. In the 
day, on the other hand, the temperature may rise above the optimum, bringing 
about a depression. In such a case the excitability in the earlier part of 
the evening may actually be greater than in the middle of the day. These 
modifications are shown in a very interesting way in the following record 
(Fig. 17) taken at the end of April. The temperature of Calcutta at this 
_J I : J : l_ 
M. 7P.M. 1A.M. 7A.M. 1 2 A..M 
Fig. 17. Diurnal variation of excitability exhibited by summer specimen. 
season often rises above ioo°F. or 38°C. Table II also exhibits, in the 
case of the summer specimen, the relation between the hours of the day, 
temperature, and excitability. 
An inspection of the record given in Fig. 17 shows that the amplitude 
of response was enhanced after 4 p.m. The temperature up to that time 
was unusually high (38° C), and there was in consequence a depression of 
excitability. After that hour there was a mitigation of heat, the tempera- 
ture returning towards the optimum. Hence we find that the maximum 
excitability was attained between the hours 4 and 6 p.m. The minimum 
temperature at night was higher in the present case than that of the experi- 
ment carried out in February ; in the former the minimum was 25-5° C, 
while in the latter it was 19-5° C. On account of this difference the night 
record in summer shows a fall of excitability which is far more gradual than 
