Septembee 6, 1912] 



SCIENCE 



305 



impressions may not be immediate, but can 

 be stored for an indefinite time in certain 

 cells of the nervous system. The regula- 

 tion of movements — whether they occur 

 instantly, after reception of the peripheral 

 impression or result after a certain lapse 

 of time; whether they are accompanied by 

 conscious sensation or are of a purely re- 

 flex and unconscious character — is an in- 

 tricate process, and the conditions of their 

 coordination are of a complex nature in- 

 volving not merely the causation of con- 

 traction of certain muscles, but also the 

 prevention of contraction of others. For 

 our present knowledge of these conditions 

 we are largely indebted to the researches 

 of Professor Sherrington. 



A less conspicuous but no less important 

 part played by the nervous system is that 

 by which the contractions of involuntary 

 muscles are regulated. Under normal cir- 

 cumstances these are always independent 

 of consciousness, but their regulation is 

 brought about in much the same way as is 

 that of the contractions of voluntary 

 muscles — viz., as the result of impressions 

 received at the periphery. These are 

 transmitted by afferent fibers to the cen- 

 tral nervous system, and from the latter 

 other impulses are sent down, mostly along 

 the nerves of the sympathetic or autonomic 

 system of nerves, which either stimulate or 

 prevent contraction of the involuntary 

 muscles. Many involuntary muscles have 

 a natural tendency to continuous or 

 rhythmic contraction which is quite inde- 

 pendent of the central nervous system; in 

 this case the effect of impulses received 

 from the latter is merely to increase or 

 diminish the amount of such contraction. 

 An example of this double effect is ob- 

 served in connection with the heart, which 

 — although it can contract regularly and 

 rhythmically when cut off from the nervous 

 system and even if removed from the body 



— is normally stimulated to increased ac- 

 tivity by impulses coming from the central 

 nervous system through the sympathetic, 

 or to diminished activity by others coming- 

 through the vagus. It is due to the readi- 

 ness by which the action of the heart is 

 influenced in these opposite ways by the 

 spread of impulses generated during the 

 nerve-storms which we term "emotions"' 

 that in the language of poetry, and even 

 of every day, the word "heart" has be- 

 come synonymous with the emotions them- 

 selves. 



The involuntary muscle of the arteries 

 has its action similarly balanced. When its 

 contraction is increased, the size of the 

 vessels is lessened and they deliver less 

 blood; the parts they supply accordingly 

 become pale in color. On the other hand, 

 when the contraction is diminished the 

 vessels enlarge and deliver more blood ; the 

 parts which they supply become corre- 

 spondingly ruddy. These changes in the- 

 arteries, like the effects upon the heart, 

 may also be produced under the influence 

 of emotions. Thus "blushing" is a purely 

 physiological phenomenon due to dimin- 

 ished action of the muscular tissue of the- 

 arteries, whilst the pallor produced by 

 fright is caused by an increased contraction 

 of that tissue. Apart, however, from 

 these conspicuous effects, there is con- 

 stantly proceeding a less apparent but not 

 less important balancing action between the 

 two sets of nerve-fibers distributed to heart 

 and blood-vessels; which are influenced in 

 one direction or another by every sensation 

 which we experience and even by impres- 

 sions of which we may be wholly uncon- 

 scious, such as those which occur during 

 sleep or anesthesia, or which affect our 

 otherwise insensitive internal organs. 



A further instance of nerve-regulation is- 

 seen in secreting glands. Not all glanda 

 are thus regulated, at least not directly;. 



