496 E. V. Cowdry, 



And this variabilit}^, in turn, is to be expected; for we must look 

 upon this system of canals as changing' in form from moment to 

 moment in the living cell in responce to physiological needs. With 

 this in mind, the slight differences, which have been urged by some, 

 between the internal reticular apparatus of Golgi and this canalicular 

 system seem of little importance. 



The neurofibrils may be regarded as the fourth of the known 

 fundamental cytoplasmic components of the nerve cell. The following 

 modification of Cajal's silver impregnation method was used for their 

 demonstration. 



I. Fixation and impregnation. 



1. Fix spinal ganglia of the pigeon for from 2 to 6 hrs. in Carnoy's 

 6:3:1 fluid. (Fixation for the same length of time in alkaline or neutral 

 95°/o ale. also gives good results.) The object of this preliminary fixa- 

 tion is the preservation of cytoplasmic structures other than neurofibrils. 



2. Wash in aq dist., 24 hrs. 



3. 1,5 °/o ap. soin, silver nitrate at 39° C for 3 days with one change. 



4. Rinse in aq. dist. and reduce in: 



pyrogallic acid 1 g, 



formalin 5 ccm, 



aq. dist. 100 ccm, in the dark for 24 hrs. 



5. Wash in aq. dist., 15 min., and add 95 "/o ale; leave for 1 hr. with one 

 change. 



6. Abs. als. for 2 hrs. with one change. 



7. Cedar oil, 2 hrs. 



8. 60" C paraffin for 3 hrs. Imbed. Cut sections 3// and fix to the slides 

 by the albumen water method. 



II. Gold toning. 



1. Pass slides down through toluol, abs. 95 "/o and 70°/o ale. to aq. dist. 



2. 0,1 °jo aq. soin, gold chloride neutralized with lithium carbonate, 2 hrs. 

 3 5°/o aq. soin, sodium hyposulphite, C. P., 5 min. This bleaches out the 



excess of silver 



4. Wash in running tap water for 6 hrs. 



5. Dehydrate, clear in toluol, and mount in balsam. 



In Cajal preparations in general and especially in this modi- 

 fication the neurofibrils are exaggerated in two ways: first, optically 

 on account of their sharp blue-black outlines against a colourless 

 ground substance; and secondly, because they form centres for the 

 deposit of silver which actually increases their bulk. 



The independence of the Nissl substance may be indicated by 

 counterstaining before dehydration (i. e. between steps 4 and 5) in a 



