G32 



PHYSIOLOGY. 



rived from food, larvae from one hatch of eggs 

 laid by a certain female insect were divided into 

 three lots and fed, in darkness, respectively 

 throughout their whole life upon (1) green 

 leaves, (2) yellow etiolated leaves, and (3) white 

 midribs of cabbage. The larvae of the first and 

 second lots became green or brown, as in nature, 

 thus proving that etiolin, no less than chloro- 

 phyll, can become the basis of the larval ground 

 color. Those fed upon white midribs of cab- 

 bage, in which neither chlorophyll nor etiolin 

 was accessible, were entirely able to form the 

 green or brown ground color. The production 

 of dark superficial cuticular pigment was, how- 

 ever, unchecked. The experiment seems, in the 

 author's opinion, to leave no doubt of the deriva- 

 tion of color from the chlorophyll of the food 

 plant. 



In experiments on the madder staining of 

 dentine by Dr. W. G. Aitchison Robertson, rab- 

 bits were fed on madder for some time and were 

 then killed, when the dentine was found to be 

 stained. When other food was supplied for a 

 time, and the feeding on madder was resumed 

 afterward, two colored layers, with an interme- 

 diate layer, were found in the dentine. 



Nervous System. A special research, to as- 

 certain what are the influences that determine 

 the activity and fatigue of the central nervous 

 mechanisms which excite the voluntary muscles 

 to action, is described by Warren P. Lombard, 

 of Clark University, Massachusetts. The ex- 

 periments were made upon the writer himself, 

 in exercising the flexor muscles of the second 

 finger, generally with the left hand, by the pull- 

 ing over a pulley of a weight, in the first experi- 

 ments of 2, and in the later experiments of 3, 4, 

 and 5 kilogrammes. They showed that, if one 

 voluntarily contracts a muscle frequently, and 

 each time raises a considerable weight with all 

 his force, his power quickly begins to lessen, 

 and sooner or later he ceases to be able to stir 

 the weight. If, however, he continues to strive 

 to raise the weight, many more or less complete 

 recoveries of power periodically occur. Through- 

 out the research the first failure to raise the 

 weight was accepted as the sign of fatigue of 

 the voluntary power. The first loss of power 

 came somewhat sooner, and the recoveries of 

 power were much more complete in the case of 

 the author than of most men whom he studied. 

 Apparently the central nervous apparatus 

 through which he sends voluntary impulses to 

 the motor nerves fatigues somewhat more quick- 

 ly than is usual, and if compelled to act rapidly 

 and vigorously tires sooner than the muscles. 

 Thus he becomes incapable of voluntarily con- 

 tracting his muscles at a time when they will 

 respond well to direct electrical excitation, or to 

 an impulse called out by irritation of the nerve. 

 This weakness, if it is to be so regarded, is com- 

 pensated for by great and rapid recuperative 

 power, and therefore never interferes with his 

 ordinary duties ; and it is noticed only in ex- 

 periments such as those described, or when he 

 attempts to exert himself to the utmost for long 

 periods of time, as in a contest in running, or in 

 a boat race. The exercise involved in the re- 

 search greatly increased the endurance of the 

 central nervous mechanism involved in the ex- 

 periments, but had apparently little effect upon 



other similar structures. The amount of fatigue 

 experienced by the central nervous apparatus in 

 producing a long series of voluntary contrac- 

 tions does not correspond with the number of 

 times that the muscle is stimulated, at least 

 when the rate is not more frequent than once a 

 second. It appears to depend rather on the 

 strength of the impulses sent out, because the 

 total height to which a given weight can be 

 lifted by such a series of contractions is a much 

 more accurate expression of the condition of the 

 central mechanism than the number of times 

 that the muscle can be contracted. Further, 

 the fatigue of the central apparatus does not 

 correspond with the amount of conscious effort 

 exerted in the work, for very many maximal 

 voluntary contractions can be made without 

 fatigue, provided the weight is small. Indeed, 

 it seems as if the strength of the impulses which 

 are sent outward to the muscle depended not 

 only on the voluntary effort, but on some influ- 

 ence which passed inward from the muscle itself. 

 The influences which have been found to affect 

 the voluntary power of the subject are to be 

 looked upon as controlling the activity and fa- 

 tigue of the special central nervous mechanisms, 

 which develop or transmit the voluntary im- 

 pulse to the nerve fibers that supply the flexor 

 muscles of the second finger of the left hand. 

 Enough experiments were made with other 

 parts, however, to show that other similar 

 mechanisms are influenced in the same way. 

 The following influences were observed : 1. 

 Those which lessen the ability to do voluntary 

 muscular work ; general and local fatigue ; hun- 

 ger; lessening atmospheric pressure, including 

 the regular and irregular variations; high tem- 

 perature, especially if associated with much hu- 

 midity; tobacco. 2. Those which increase the 

 ability to do voluntary muscular work ; exer- 

 cise ; rest, and especially sleep ; food ; increas- 

 ing atmospheric pressure, including regular and 

 irregular variations ; alcohol. 



Though quantitative results as to the relative 

 efficiency of these different influences can not 

 be given, something as to their relative effect- 

 iveness may be stated. Exercise acts in the 

 same direction as sleep and food, and is a very 

 potent factor. While the two latter simply act 

 to restore the strength, exercise increases the 

 power. Sleep has a greater effect than food, 

 and is much more beneficial than waking rest, 

 perhaps because the restorative processes then 

 go on unopposed. The supply of nutriment 

 only fulfills one of the requirements for the re- 

 covery of strength. A rising barometer favors 

 the action of exercise, sleep, and food to in- 

 crease the power, while a falling barometer 

 opposes them, and may overcome their influ- 

 ence and lessen the strength. -Though the 

 regular diurnal changes in atmospheric pressure 

 undoubtedly influence the writer's power, the 

 effect is a delicate one, which is readily obscured 

 by more potent influences. Tobacco and alco- 

 hol act very vigorously. Tobacco may prevent 

 the effect of a rising barometer gr of food from 

 showing itself, and seems even to lessen the 

 strengthening effect of exercise. Alcohol, in 

 small amounts, increases the strength to a 

 marked degree, even when the barometer is fall- 

 ing. The effects of tobacco and alcohol, there- 



