GLYCOGEN IN THE NERVOUS SYSTEM 459 
glycogen in any of the embryo pigs studied, thus agreeing with 
the statements of Bernard that glycogen is relatively late in 
appearing in the liver. 
In the alimentary canal the glycogen passes as a kind of wave 
along the tube, commencing at the mouth and passing in order 
to the esophagus, the stomach, and, as the villi commence to 
appear, extending along down the small to the large intestine. 
The investigation of human embryos for glycogen is carried 
on with more uncertainty than is that for other forms owing to 
the difficulty of obtaining material in the different stages which 
can be fixed in the alcohol before the glycogen becomes dissolved. 
However, owing to the courtesy of Dr. Mall, and several of my 
old students, some fairly normal human embryos fixed in alco- 
hol before all of the glycogen was dissolved, have been studied, 
and I have found the glycogen distributed among the organs and 
tissues as described for mammals generally. 
In the nervous system, the only unmistakable situation in 
which it has been found up to the present is in the choroid plexus 
of a 19 cm. human fetus and in the choroid plexus and the cells 
of the raphé of the medulla oblongata of a 35 mm. human em- 
bryo preserved in strong alcohol. The endymal cells showed the 
same abundance of glycogen that has been found in the embryo 
of the cat and pig. A figure of this human plexus with the 
glycogenated endymal cells is given in the accompanying plate 
(fig. 10). It is confidently expected that when the proper ma- 
terial can be obtained glycogen will be found in the human 
nervous system and organs of sense, as with other mammals. 
CONCLUSIONS 
From the data given above it is believed that the following 
conclusions may be fairly drawn: 
1. The production and use of glycogen is one of the properties 
of nervous as of all other forms of protoplasm. 
2. Glycogen is an essential accompanier of nervous as of all 
other tissues in their histogenesis, especially in the transition to 
their definitive and functional stage. 
