NEUROFIBRILS All 



leave for twenty-four hours. Wash in repeatedly-changed distilled 

 water for twenty-four hours, pass through alcohols and xylol 

 into paraffin, and cut sections. Mount, after removing paraffin, 

 without further staining, 



Paravicini {Boll. Mus. Z. Anat. Comp. Torino, xx, 1905, p. 1) 

 fixes and mordants in the dark, and differentiates after staining with 

 extremely weak hydrochloric acid. 



ToMASELLi {Ztschr. iviss. Mikr., xxiii, 1906, p. 421) fixes spinal 

 ganglia for six to seven hours in absolute alcohol 100 c.c. with 4 to 5 

 drops of ammonia, and then transfers them for two days into pure 

 pyridine to be repeatedly changed, the vessel with the pieces being kept 

 at 36° to 37° C. After washing for two to three hours in running tap- 

 water, he continues as in Donaggio's Method III. 



For the cricticism of Jaderholm, see Arch. mikr. Anat., Ixvii, 1906, 

 p. 108 ; and for that of Montanari, Ztschr. miss. Mikr., xxviii, 1911, 

 p. 22. 



1011. Ramon y Cajal's Methods. Introductory. It has been 

 said by some authors that Cajal's methods were originally only 

 modifications of the photographic process of Simarro. The 

 criticism is unjust because even the first formula of Cajal differs 

 so profoundly from Simarro 's process as to form an entirely new 

 method. One cannot, however, deny the existence of a certain 

 similarity of conception between the two processes in so far as 

 both are based on the silver-reducing power of certain photographic 

 reagents. For this reason it has been thought expedient briefly 

 to describe here Simarro's process, which though uncertain in its 

 results, may still be of some value to elucidate certain histological 

 questions. 



Simarro's Process {Rev. Trim. Micr., v, 1900, p. 45) consisted in 

 poisoning animals with subcutaneous injections of solutions of sodium 

 or potassium bromide or iodide in order to impregnate their living 

 nervous tissues with one or the other of these salts. As soon as the 

 animals showed that the poisoning had reached its maximum they were 

 killed and their central nervous system removed in the photographic 

 dark room. Small pieces were then immersed in a solution of silver 

 nitrate, which, by combining with the bromine or iodine with which the 

 tissues were impregnated, gave rise to the formation of silver bromide 

 or iodide, which is easily affected by light. Sections were then made 

 (always in the dark room), best by means of a freezing microtome, and 

 exposed for a little while to light. There remained only treating them 

 with a photographic developer, such as hydroquinone, pyrogallol or the 

 hke, and fixing them with sodium hyposulphite and so on, as if they 

 were photographic plates ; they were lastly washed, dehydrated and 

 mounted in the usual way. 



One can easily understand the many drawbacks of such a method and 

 the reason for which it was abandoned as soon as Cajal published in 

 1903 his first reduced silver methods. From that time onwards, Ramon 

 y Cajal continued improving them and adding new formula;, which he 

 himself summarised in a special article of his Trah. Lab. Invest. Biol., 

 Madrid, viii, 1910, on which the following account is based. The num- 

 bering is that of Ramon y Cajal. 



