xlii Journal of Comparative Neurology. 



Bolton's results with human tissue, though it is noteworthy that his 

 finest preparations were obtained by simply mordanting for a short time 

 sections of the formalin-hardened brain, while with the fish tissues this 

 method in my hands gave negative results and the tissue must be fixed, 

 as well as mordanted, in the iron salt. 



CONCLUDING REMARKS. 



Extended commentary upon these experiments is unnecessary, as 

 the results speak for themselves so far as practical utility is concerned 

 and it is not my purpose to enter into an elaborate discussion of the 

 theory of the Weigert stain. The ground covered in the experiments 

 was, as has been stated, determined wholly by the practical require- 

 ments of a definite research ; nevertheless the peculiarities of the tis- 

 sues upon which the work was done are such as to cast some light upon 

 the nature of the staining processes. 



In this research I have found, as others before me have done, that 

 the fish tissues are refractory to a surprising degree. This does not 

 accord with my own earher experience, for, in the course of the prep- 

 aration of an extended series of teleostean brains by ordinary methods 

 (especially Delafi eld's hgematoxylin) made several years ago in connec- 

 tion with my brother, it was easy to obtain the most elegant prepara- 

 tions, — preparations which could not be excelled in any other group of 

 vertebrates. But in the present case there were not only the special 

 difficulties mentioned in the introductory paragraphs, but the presence 

 of the body musculature in the sections imposes other peculiar condi- 

 tions. It seems that the teleostean muscles and the myelinic nerve 

 sheaths react toward the hcematoxylin stains very similarly, for they 

 decolorize at very nearly the same time. It was found, for example, 

 in every case where the decolorizer of Pal was tried that the nerves 

 clear before the muscles and in other cases they often clear at about 

 the same moment. This peculiarity destroys the value for peripheral 

 nerves of a number of processes which are very satisfactory centrally. 

 It also sheds some light upon the nature of the staining process. 



In the paper by Bolton to which reference has already been made, 

 this author concludes, as a result of an extensive series of experiments 

 upon human brain tissue which had been hardened for several months 

 in five per cent, formalin, that, "the AVeigert-Pal process is not a spe- 

 cific method for the staining of medullated nerve fibers with hcema- 

 toxylin but is a method of dyeing fibrils which comprises three distinct 

 operations : the mordanting of the fibers, the formation of a lake in 

 them, and finally, the removal of the stain by oxidation from nearly 

 every other part of the complex tissue under treatment." 



