20 



SCIENCE. 



[N. S. Vol. XV. No. 366. 



touched. If the ganglion be removed the ani- 

 mal will still carry out this reflex. But care- 

 ful study shows that there are differences be- 

 tween the action of the normal animal and 

 the one which lacks its ganglion. In the latter 

 the threshold of stimulation is higher and the 

 reaction-time greater. From this Professor 

 Loeb concludes that Hhe nerves and ganglion 

 only play the part of a more sensitive and 

 quicker conductor for the stimulus.' 



The tentacles of Metridium in the food-tak- 

 ing activity of the animal move in such a way 

 as to bring the object with which they are in 

 contact to the mouth. The action is one of ap- 

 parent adaptation, and one would scarcely ex- 

 pect to see the same kind of a reflex occur after 

 ' the tentacle had been cut from the body. Such, 

 however, is the result of the experiment; no 

 diiference between the action of the tentacle in 

 normal relation to the nervous system and that 

 which has been isolated is observable. We 

 have to conclude, therefore, that the action is 

 determined by the properties of the protoplasm 

 of the tentacle itself, and not by special proper- 

 ties of the nei'vous tissues. 



Other observations prove that certain worms 

 when deprived of their brains are able to move 

 spontaneously. As a case in point, the fresh- 

 water Planarian, Planaria torva, is sensitive to 

 stimulation by light. To any increase in in- 

 tensity it responds by movement. It also se- 

 lects the darkest region of a dish in which it is 

 left. When the anterior portion of the body 

 is cut off it is found that the brainless por- 

 tion will give the same responses to light as the 

 normal animal. And the only significant fact 

 in favor of the influence of the brain upon 

 such activities is that the reaction-time of the 

 brainless animal is longer. 



Of the reflexes of higher animals that are 

 known to be in part at least independent of 

 the brain and cord are the movements of the 

 iris, the bladder, rectum, blood vessels, respira- 

 tory organs, etc. Experiments upon fishes, 

 frogs and dogs have established the independ- 

 ence of many of their reflexes. In one instance 

 the whole brain and spinal cord of a larval frog 

 were destroyed without interfering with spon- 

 taneous movements. There are so many ob- 

 servations of this kind for the vertebrates that 



one cannot question the general truth of Pro- 

 fessor Loeb's conclusion. As he states, those 

 instances in which the reflex is interfered with 

 by the destruction of the nervous system are 

 explicable by the fact that the only existing 

 connection between the sense organ and the 

 muscle has been broken. Establish any kind 

 of protoplasmic connection between the region 

 in which the disturbance arises and the motor 

 apparatus, and the appropriate reflex will be 

 executed. 



But the fundamental experiment for the 

 proof of the independence of reflexes is that 

 made by Professor Loeb upon isolated muscles. 

 Ho has shown that muscles containing no gan- 

 glion cells will beat rhythmically when placed 

 in a pure sodium chloride solution of the same 

 osmotic pressure as the blood. To put the 

 matter in his words, "It is not the presence or 

 absence of ganglion cells which determines the 

 spontaneous rhythmic contractions, but the 

 presence or absence of certain ions. Na ions 

 start or increase the rate of spontaneous rhyth- 

 mical contractions ; Ca ions diminish the rate 

 or iiJiibit such contractions altogether." Now 

 it is clear that to prove the isolated muscle ca- 

 pable of responding to stimuli is to establish 

 the thesis which has been stated. 



The conception of the nervous system as a 

 series of more or less intimately related cen- 

 ters, each with its own special function, arose 

 and found an observational basis in the many 

 experiments on localization. Certain parts of 

 the brain apparently control certain groups of 

 muscles. This is undoubtedly true, but Pro- 

 fessor Loeb attempts to show that the concep- 

 tion as a whole is false. From comparative 

 morphology and physiology comes abundant 

 evidence of the segmental theory of the nerv- 

 ous system. In the Annelids, for example, the 

 segments, each with its ganglion and nerves, 

 are to a certain extent independent organisms. 

 Each ganglion in this ease functions in con- 

 nection with a very definite portion of the 

 worm. 



"The so-called centers of the cerebral cortex 

 are merely the places where the fibers from 

 single segments of the central nervous system 

 enter." If the spinal cord of a dog be cut it 

 will be found, after the shock of the operation 



