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Proceedings of the Royal Society of Edinburgh. [Sess. 
of 41*2° and 41 ‘4° — -much below the general average — and this brought the 
mean figure for the seven down to 41*84°, as compared with 42*24° for the 
same birds on June 27, 1910. If all the birds in this condition had been 
excluded, the figures would be practically the same as on the corresponding 
dates of the previous year. Another cause of the irregularity is the small 
number of individuals under observation, since the larger the number from 
which the mean figures are obtained the smaller is the effect of individual 
and accidental variations on the mean temperature. 
We now come to the most important point, and that is a consideration 
of the effect of the annual curve of egg-production on the body temperature 
curve. The curve of egg-production may be taken as the vitality curve of 
the hen, since it is functionally most active when this curve reaches its 
maximum and least so at its minimum. The curve of egg-production 
attains its highest point in April and May; the temperature curve in June, 
July, and August. Here the hot weather of summer is a disturbing 
influence, since but for this the body temperature curve might have fallen 
parallel with the egg-production curve, but if we compare the body tempera- 
ture in May when egg-production is at its highest, with that in October 
when it is almost at its lowest, we find that the two figures are nearly 
identical. The mean for 114 hens in May is 41 *93°, and for October 41 ‘90° 
and on the days in these months (1910) on which the hens were examined 
the weather conditions were fairly comparable, — if anything, both as regards 
sunlight and external temperature, they were in favour of May (see weather 
table, pp. 132-133). 
It would thus appear that in the domestic fowl the annual cyclical 
change represented by the egg-production or vitality curve does not affect 
appreciably the body temperature, and that, if the effect of muscular exercise 
be excluded, its variations are due to influences acting on the body from 
without rather than from within. 
The upper and lower limits, and the annual temperature range for the 
different breeds examined, are as follows, counting all the birds on which 
observations were made for one year : — 
Rhode Island Reds .... 42*31 - 4T69 = 0‘62 range 
White Wyandottes .... 42*43 - 41 *77 = 0 66 ,, 
Buff Orpingtons .... 42*33-41*63 = 0*70 ,, 
Barred Plymouth Rocks . . . 42*30 - 41*53 = 0‘77 ,, 
Brown Leghorns .... 42*67 - 41*80 = 0*87 ,, 
White Plymouth Rocks . . . 42'55 - 41*67 = 0*88 ,, 
Although there is little difference amongst the six varieties, it may be stated, 
in a general way, that the heaviest and most lethargic birds have the lowest 
