8 H. V. NEAL 



rological investigation, the results by no single neurological stain, 

 however specific, may be wholly trusted. The methods suited 

 to demonstrate the neurofibrils in vertebrate embryos give very 

 unsatisfactory pictures of cell boundaries and relationships. But, 

 as a basis for theoretical conclusions, the cellular relationships 

 are quite as important as phases of differentiation of neurofibrils. 

 Moreover, it must not be forgotten in the enthusiasm created 

 by the newer discoveries that, provided embryological material 

 be abundant, the identification of an embryonic structure as 

 nervous may be determined by tracing its fate through succes- 

 sive stages of development. The demonstration of neurofibrillae 

 therefore is not absolutely indispensable in the determination of 

 its nervous character. 



In the course of the present study different methods have 

 been used. Among those which have given the best results 

 are Cajal's nitrate of silver, Paton's modification of Bielchowsky's 

 method, Held's molybdic acid — hematoxylin stain and vom 

 Rath's picro-acetic-osmic-platinic chloride — pyrogallic acid treat- 

 ment. All the drawings in plates 1 to 8 of this paper were made 

 from preparations by the latter method. They have been con- 

 firmed by observations upon material in which the neurofibrillae 

 were specifically stained. 



The Vom Rath ('95) method is as follows: 



1. Fix in the dark for one to three days in the following mixture 

 (use plenty and change each day) : 



Saturated and filtered solution picric acid 200 cc. 



Glacial acetic acid 2 cc. 



Platinic chloride (dissolve in 10 cc. water) 1 gram 



Osmic acid 2 per cent 25 cc. 



OxN-ing to the great brittleness of embryos fixed in this fluid all changes 

 of liquid should be made A\ith pipette in the same dish, avoiding as 

 far as possible any movement of the embrj-os. 



2. Stain in 0.5 per cent pyrogallic acid in the dark for twenty-four 

 to forty-eight hours ^^dth several changes. 



3. Grades of alcohol from 35 per cent slowly by the siphon capillary 

 drop method to avoid shrinkage. Xylol, to which paraffin is added 

 as it dissolves. 



4. Imbed in rather hard paraffin of best quality. 



5. Thin sections, not over 8 micra, preferably 4 to 6 micra. 



