DEVELOPMENT. OF FOURTH DAY 521 



Off hand, one might say, that as nerves carry impulses to all mus- 

 cles, and as there are nerves in the heart muscle, the action must be 

 nervous. 



Nerve fibers grow into the heart muscle from the nerve cells close 

 by, but the very finest nerve stains known, have been unable to demon- 

 strate that there are any nerves whatever in the heart muscle at the time 

 of its earliest beating. It may be objected that however fine our nerve 

 stains may be, they are not sufficiently so to demonstrate possible nerve 

 cells or parts of nerve cells. And, that if we improve in our technical 

 ability by obtaining new stains, we may expect to find nerve-cell-sub- 

 stance heretofore unseeable. This objection is not well taken, because 

 if any muscle be removed from the body and placed in normal salt solu- 

 tion, the muscle fibers do not lose their contracting ability, although 

 in a few days the nerves degenerate and can be dissected out. If, then, 

 our present stains do show the nerve fibers clearly in embryos, and 

 these can be seen to be in exactly the same position as in the- adult heart^ 

 as demonstrated by the experiment just cited, it is quite reasonable to 

 assume that the stains do show all the nerve fibers that are actually 

 present. If this be true, we can demonstrate that all such nerve fibers, 

 which normally take a stain, have been destroyed. But, the new nerve- 

 less muscle still contracts and expands. 



It could, of course, be argued that in so far as this is embryonic 

 material not yet far removed from the germ plasm, that, therefore, every 

 particle of the embryonic material still retains some of the undifferen- 

 tiated nerve cells, and consequently every part of the embryo does 

 actually retain some slight nervous substance which may, under extra- 

 ordinary circumstances, be brought forth. 



This objection is overcome by an experiment performed some years 

 ago by taking a portion of the adult intestinal tract, chopping it up very 

 finely, and placing it in a test tube. Notwithstanding the fact that it 

 was thoroughly chopped up, this substance still was ab 1 e to digest food 

 placed in the tube with it. Those who insist upon all action being 

 nervous in type, then contended that the different particles of the intes- 

 tine still retained some of the essential parts of the nerve cell, so that, 

 notwithstanding the parts being cut up into very tiny particles, the 

 essential nervous elements were still doing the work. 



A portion of intestine was then kept in a chemical medium similar 

 to that mentioned in the heart-experiment, and, as with the muscle-ex- 

 periment, the nerves degenerated and were dissected out, but the intestine 

 itself continued performing its normal functions. 



If the tough adult nerve-structures are so easily degenerated 

 in a normal salt solution, it is surely safe to assume that the hundred- 

 fold more delicate embryonic nerve structures will also be destroyed in 

 such a medium. 



It will be remembered that the heart grows as a simple straight 



