Eoss Granville Harrison 217 



While it has been emphasized in the foregoing that the bnilding up 

 of the mnscnlatnre takes place normally even in the absence of connec- 

 tion with the nervous system, it is not to be lost sight of, that in all of 

 the experiments certain signs of interference with normal development 

 and of degeneration make themselves apparent. The general retarda- 

 tion of the development of embryos reared in acetone-chloroform may, 

 however, be accounted for, as pointed out above, by the direct action of 

 the drug upon metabolism and upon the heart. The most noticeable 

 degenerative change in the embryonic muscle, the appearance of vacuoles 

 in the axial sarcoplasm, may also be explained as due to disturbances in 

 the circulation. That the vacuolization of the embryonic fibers is not 

 due specifically to the removal of nervous influence is shown clearly by 

 the fact, to which Dr. Knower has called my attention, that an exactly 

 similar condition supervenes in the musculature of frog embryos from 

 which the heart had been removed at an early stage. Much of the inter- 

 ference with the normal processes of development may therefore be set 

 down as due to influences other than the changed relations with the ner- 

 vous system, though it is not impossible that the disturbances are due 

 to some extent to the latter cause. This would not be remarkable, how- 

 ever, in view of the well-known fact that in the adult a muscle undergoes 

 atrophy after its nerve supply is cut off.' 



We must, in fact, consider the embryo not merely as a developing 

 organism, in which the parts are important potentially, but also as an 

 organism, which in each stage of development has functions to perform 

 that are of importance for that particular stage. If these functions are 

 interrupted, as they are in the present experiments, we can but expect 

 to find, that side by side with the constructive processes which build up 

 a muscle fiber out of an undifferentiated muscle cell, and which, as the 

 experiments show, take place quite independently of the nervous system 

 or the stimulus of function, there also take place certain degenerative 

 changes due to the absence of these influences. The results of experi- 



" The morphological changes which take place in a muscle after neurotomy 

 have been the subject of numerous investigations, of which a full review 

 has been given by Stier, 97. The most pronounced changes are diminution 

 in the caliber of the fibers and proliferation of the sarcolemma nuclei. Ricker 

 and Ellenbeck, 99, find also vacuolization of the fibers and other signs of 

 oedema. Ricker, 01, explains the changes which take place as due primarily 

 to the interference with the normal working of the vasomotor apparatus 

 of the muscle. De Buck and de Moor, 03, who have studied the subject most 

 recently, emphasize the regressive changes of the muscle fiber itself, i. e., 

 its return to the embryonic condition, and consider the changes to be due 

 to the lack of functional stimuli. 

 16 



