June 22, 1917] 



SCIENCE 



621 



arise the cool deliberations of the man of 

 science, the dreams and aspirations of the 

 poet, the passion of the religious enthusi- 

 ast, and, when abnormalities intervene, the 

 ravings of the madman. Contrary to an- 

 cient belief, the spleen does not engender 

 temper, nor do the affections flow from the 

 heart. These and all other like attributes 

 proceed from the brain. And yet the old 

 traditions have so strong a hold upon us 

 that I doubt whether any modern suitor 

 would forward his cause by offering to the 

 lady of his choice the real organ of his af- 

 fection, his cerebral cortex, rather than his 

 heart. 



Accepting the modern view that the con- 

 scious life of man is not a function of his 

 body as a whole but an activity limited 

 strictly to his nervous system, it follows 

 that the evolution of this system becomes a 

 question of special interest. In man and 

 the other higher animals this system con- 

 sists of a most intricate collection of trans- 

 mitting fibers, end-stations, centers and the 

 like so disposed as to receive and record 

 the influx of surrounding changes and to 

 respond to these by appropriate movements. 

 The light of a friendly countenance reaches 

 us through the eye and a word of salutation 

 through the ear and off comes the hat in re- 

 sponse. "When we scrutinize more closely 

 the machinery of these operations, we find 

 it simple in outline, though inconceivably 

 intricate in detail. There are first of all the 

 sense organs of the body, the eyes, ears, 

 nose, mouth and so forth each attuned to a 

 particular set of influences or stimuli and 

 each delivering to the central organs evi- 

 dences of the momentary states of these 

 stimuli in the exterior. Next are the cen- 

 tral organs, the brain, spinal cord and the 

 like, parts that receive the flood of sensory 

 information from the outer world and pass 

 it on unnoticed or store some remnant of it 

 as a part of life's experience. Last of all 



are the voluntary muscles set in action by 

 impulses from the central apparatus and 

 capable of performing the thousand acts 

 good or ill that make us the responsible be- 

 ings that we are. These in gross outline are 

 the three great categories of our nervous 

 machinery, or better, of our neuromuscular 

 machinery, for muscles are necessarily an 

 integral part of this chain. When such a 

 chain goes into action, sense organ, central 

 nervous organ and muscle, we speak of this 

 as a reflex, for it resembles light in that it 

 passes from an external source inward to a 

 central organ whence it is reflected, so to 

 speak, outward to the muscle. 



If we examine the nervous systems of ani- 

 mals lower than man, we find in them the 

 same three categories of parts. All the ver- 

 tebrates from the mammals to the fishes 

 have sense organs, central nervous organs 

 and muscles. The same is true of the snails, 

 the clams, the insects, the crabs and many 

 others. Even the worms possess these three 

 classes of organs, though with less differen- 

 tiation as a rule than in the higher animals. 



But, when we study the jelly fishes, the 

 sea anemones, or hydroids, the case is dif- 

 ferent. Here we meet with an obvious sim- 

 plification and what is noteworthy is that 

 all three parts are not equally reduced, but 

 that one, namely, the central organ, has 

 suffered almost complete obliteration. In 

 these lowly creatures the sense organs, 

 either in the definite form of eye spots and 

 the like, or as broad receptive surfaces with- 

 out great specialization, are superimposed 

 almost directly upon the more deeply 

 seated muscles. Such animals often have 

 not even a trace of an intervening nervous 

 organ that could be called a central organ. 

 The sense organs may thus connect directly 

 with the muscles. Obviously under these 

 circumstances the sense organs lack entirely 

 that function that they showed in so 

 marked a degree in the higher animal. 



