Implications of the Theories of Nerve Action 197 



limbs arise that the movements of these members are very nat- 

 urally affected." 13 It is the interdependence fore-and-aft 

 of reflex activities like those here indicated, that is, of the 

 fore limbs acting with the mouth, and the hind limbs with 

 the fore limbs, that suggested to Loeb the idea of "chain 

 reflexes," a conception of special interest from our stand- 

 point. 



That the segmental mode of functioning of the vertebrate 

 nerve axis is not limited to the lower portion of the great 

 vertebrate phylum is, as Loeb points out, shown by such 

 investigations as those of Goltz, and of Goltz and Ewald on 

 the dog. These are given so fully in the larger text-books 

 of physiology and are thereby so readily accessible to all 

 specially interested in the subject, that a very brief presen- 

 tation will suffice. 



Two main groups of reflex centers in the nerve cord are 

 made out, the cervico-thoracic and the lumbo-sacral. The 

 first group contains the center for movements of the an- 

 terior limbs, for respiratory movements, for acceleration 

 of heart action, for dilation of the pupil of the eye, and for 

 several other activities at the anterior end of the body. The 

 lumbo-sacral group contains the center of movements for 

 the posterior limbs, for control of the anal sphincter, the 

 activities of the generative organs, and several other parts. 



The existence of such centers in the dog's cord w r as proved 

 by section of the cord at different levels under the most 

 careful operative conditions. Had the investigation stopped 

 with experiments of this sort the facts brought out might 

 have been interpreted as confirmatory of the "seat" notion 

 of a nerve center. When, however, it was discovered that a 

 dog from which most of the cord is removed may live for 

 many months in a good state of health, all the vegetative 

 functions being carried on almost typically, it became clear 

 that the various centers of the cord are not the seats of life 

 activities in any such fundamental sense as was earlier 



