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AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



each group, these latter being separated by portions of the curve in which the 

 contractions are very small or wanting (see Fig. 208). (See General Physiology 

 of Nerve and Muscle, p. 126.) 



Daily Rhythms. Within the cycle of the astronomical day the progress 

 of events leading to fatigue is not a steady one. Lombard 1 found that if the 

 capacity for voluntary eifort was measured by the amount of work which could 

 be done by voluntarily contracting the flexor muscles of the index finger before 

 the first failure to respond to a voluntary stimulus appeared, then the curve 



FIG. 209. Showing at each hour of the day and night how many centimeters a weight of 3000 grams 

 could be raised by repeated voluntary contractions of the forefinger before fatigue set in. The curve is 

 highest at 10 to 11 A. M. and 10 to 11 p. M. ; lowest, 3 to 4 p. M. and 3 to 4 A. M. Circle with dot, observation 

 made just after taking food; square with dot, smoking; *, work done eight minutes after drinking 15 

 cubic centimeters of whisky (Lombard). 



expressing this capacity for voluntary work throughout the day was repre- 

 sented as in Fig. 209. Briefly, the curve shows two maxima, at 10 P. M. and 

 10 A. M., with two minima midway between them. In general the immediate 

 effect of taking food is to increase the work done by the subject. Alcohol has 

 the same effect, while smoking produces a decrease. 



Further, from day to day this capacity for work was influenced by a num- 

 ber of external conditions temperature, barometric pressure, etc. 



Time taken in Central Processes. All processes in the nervous system 

 take time, and are for the most part easy to measure. The rate of the nerve- 

 impulse has already been given. It has also been noted that in passing through 

 the body of a spinal ganglion-cell the impulse suffers some delay. When, 

 1 Journal of Physiology, vol. xiii., 1892. 



