Charles Russell Bardeen 247 
Schwann. If muscle-fibres with the terminal nerves running to them 
be hardened in osmie acid or impregnated with gold-chloride and then 
digested in pancreatin, the protoplasm of the muscle-fibre disappears, 
but the sarcolemma, the sheath of Schwann, the myelin sheath, and 
some portions of the nerve-endings, probably the stroma, are left undi- 
gested. With care these digested specimens may be stained and mounted 
in glycerine or in balsam. In all successful specimens which I have 
prepared in this way, I have found the sheath of Schwann inseparably 
connected with the sarcolemma and the undigested portion of the end- 
plate closely united to and apparently on the under surface of the latter. 
The most satisfactory specimens are obtained with the muscles of frogs. 
See Fig. 11. It seems probable that the sarcolemma is formed through 
the action of the surface nuclei of the muscle-fibre, in response, possibly, 
to stimuli arising from the union of the nerve with the muscle-fibre; 
and it is so formed that it incloses that portion of the nerve which is 
spread out over the protoplasm of the muscle. 
Various stages in the development of end-plates in muscle-fibres of 
mammals were described in 1892 by Mays. ‘To the descriptions in 
Mays’ most valuable paper I have nothing to add. In a study of the 
development of end-plates in pigs, mice, and guinea-pigs, I have séen 
specimens corresponding to many of Mays’ pictures. In certain respects 
what I have seen corresponds to the description given by Galeoti and 
Levi of the formation of end-plates on the regenerating muscle-fibres of 
the lizard. This last paper and that of Mays both contain good summa- 
ries of the literature on the subject of the development of nerve-endings. 
b. Internal Differentiation of the Nerves. 
From the neuroblasts and from the spinal ganglion cells processes of 
considerable thickness are sent out into the peripheral nerves. It has 
been mentioned above that these processes soon begin to give rise at their 
extremities to groups of fibrils. During the early stages of development 
these fibrils may either be gathered in small compact groups, each of 
which represents an axis-cylinder process or they may be so scattered 
within the nerve that it is impossible to distinguish definite groups of 
fibrils corresponding to axis-cylinder processes. It seems probable that 
these embryonic fibrils increase in thickness as well as in length and in 
turn give rise at their extremities to new groups of fibrils. It is possible 
6 The capillary cells and the white fibrous tissue are also left undigested. By 
staining heavily in Delafield’s haematoxylin and then counter-staining in Congo-red, 
the sarcolemma, the capillary cells and the sheath of Schwann take a blue tint, and 
the fibrous tissue a red. 
