An inspection of the record given in Fig. 29 shows that the amplitude of response was enhanced after 4 p.m. The temperature up to that time was unusually high (38°C.),
Fig. 29. Diurnal variation of excitability exhibited by summer specimen.
and there was in consequence a depression of excitability. After that hour there was a mitigation of heat, the temperature 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 experiment 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 that obtained in spring. The excitability is here not totally abolished in the morning, but reaches a minimum
