100 Journal of Comparative Neurology. 



fects were principally due to the well known slowness with 

 which osmic acid penetrates and to the distortion of the nerve 

 fibers which it often produces either by a swelling effect upon 

 the myelin sheaths or by a shrinkage of the perineuric investment 

 of connective tissue. The myelin sheath seems to undergo 

 some form of disintegration shortly after death and unless the 

 osmic acid penetrates the sheath before this occurs, the reduc- 

 tion of the osmium is incomplete and indefinite structures are the 

 result. To avoid this the nerve must be exposed to the action 

 of the reagent as quickly as possible. For the entire ten spinal 

 nerves, it was found difficult to accomplish this, especially in 

 case of the intervertebral portions of the nerves, without some 

 pulling or crushing or the loss of some of the smaller dorsal 

 branches. It is well known that the action of osmic acid upon 

 the medullary sheaths of fibers which have been injured results 

 in very abnormal appearances. 



Little difficulty was met in obtaining with osmic acid well 

 stained sections from those portions of the nerve roots lying 

 free in the spinal canal, or in obtaining fairly satisfactory sec- 

 tions from that part of the nerve trunk lying exposed in the 

 body cavity. The great difficulty was experienced in getting 

 sections well blackened and intact of those portions of the nerve 

 immediately central and distal to the spinal ganglion. Even if 

 removed from the intervertebral foramen without injury or loss 

 of some of the branches, there still remained the periganglionic 

 capsule of connective tissue and the "periganglionic gland." If 

 this was left on, it interfered with the penetration of the osmic 

 acid and the contraction of the capsule produced by the reagent 

 resulted in an injurious condensation of the nerve fibers which 

 it enclosed. If removed, its removal in the fresh state was well 

 nigh impossible without injury to the nerve. The use of osmic 

 acid being thus beset with difficulties, other methods of treat- 

 ment were resorted to. However, after trying both the Pal- 

 Weigert method and a modification of the iron haematoxylin 

 method, neither of which gave preparations so suitable for pho- 

 tographing nor, after the required decolorization, preparations 

 in which the small fibers appeared satisfactorily distinct, it be- 



