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The third influence to which the temperature of animals is 

 subjected, is the period of the day. On this subject accurate 

 observations have not been made : day and night to animals 

 are properly their periods of sleeping and waking. The 

 greater power of resisting cold in the former state, must, 

 from their own experience, be familiar to all. 



The fourth influence is that of the season of the year. 

 The power of generating heat is modified by season, in a 

 remarkable degree, in warm blooded animals. With the few 

 exceptions of the hybernating animals, it increases with the 

 cold and diminishes with the heat. This might be inferred 

 a priori from the fact, that, to preserve an equal temperature 

 under a greater degree of cold, a greater quantity of heat is 

 necessary, and as this does not arise from greater activity of 

 function, it must be from greater power. Edwards performed 

 the following experiments on full grown and active sparrows : 

 Earthenware vessels were plunged into a mixture of ice and 

 water, consequently their temperature was reduced to 32°. 

 A gauze diaphragm was placed in them, upon which the 

 birds were laid, and a covering over all, upon which was 

 piled broken ice; means were taken to secure a free current 

 of air through the apparatus, and caustic potash was placed 

 in it to absorb the carbonic acid formed. In winter, in the 

 month of February, five adult sparrows were, at the same 

 time, included in the apparatus. At the end of an hour 

 they were found, one with another, to have lost 0°.72 

 Fahrenheit only, some of them having suffered no loss of 

 temperature, others having lost as much as 1°.8 Fahrenheit. 

 The temperature of the whole then remained stationary to 

 the end of the experiment, which lasted three hours. In 

 the month of July, the same experiment was performed 

 on four adult sparrows : at the end of an hour their heat 

 had undergone a mean depression of 6°. 5 Fahrenheit, the 

 extremes being 11°. 7, and 3°. 6. In the winter experi- 

 ments the animals were transferred from a warm room into 

 the apparatus, so that no difference could arise in the 



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