154 THE DISEASES AND DISORDERS OF THE OX. 



Again, if we compare together day and night, we find that 

 the day-time is characterised by the presence of sun-light and 

 of sun-heat, and that in the day-time there have been manifested 

 by animals for untold ages the associates of work. The pulse 

 and respirations are more frequent in the day-time, and there 

 is a separation of a greater amount of carbonic-acid gas and 

 urea. The body temperature also is higher. It has been shown 

 by Dr. D. A. Gresswell that light stimulates the action of the 

 heart, and that tropical heat is accompanied by rise of the tem- 

 perature of the body. The factors, then, which constitute day, 

 external or inorganic, and internal or organic, are each and 

 all concerned in adding to the activity of vital processes. The 

 external factors (light and heat), in reference to the internal 

 factors, stand, of course, in the relation of cause to effect, not 

 only directly, but also indirectly, since they afford opportunities 

 for working which are not present at night. 



In short, a rhythm has thus been established in organisms 

 in regard to day and night, and this rhythm is, moreover, still 

 kept up, even when some of the factors concerned in the 

 causation of it are altered, just as also the variations in the 

 frequency of the pulse which have reference to meal-times 

 persist, even if we pass the whole day without food. For 

 example, if we commence working by night and resting during 

 the day, it is some time before we obtain a reversal of the 

 temperature curve, and the reversal is probably never quite 

 complete. If, on the other hand, we proceed gradually from 

 one meridian to the antipodal meridian, we gradually 

 change all the associated factors of what was our day for 

 those of night, and under those circumstances the daily curve 

 of body temperature persists, although there are facts which 

 tend to show that the older-established rhythm does not yield 

 with the very best grace. Moreover, in pyrexial conditions 

 the body temperature tends to rise and to fall at the same 

 times as it does in health. Again, the fact that pain is so 

 generally more intense by night than it is during the day, 

 and the greater likelihood of a febrile patient being restless 

 and afterwards delirious by night than by day, though the 

 temperature be no higher, may be compared with the fact that 

 in health, when hot during the night, we cannot sleep; while 

 •we may, even when hotter, be able to sleep by day. Day 



