xxxi'v Journal of Comparative Neurology. 



A. — Hermann's Fluid. 



31 M. Specimens fixed for from 2 to 13 days in Hermann's fluid, fre- 

 quently changed, were cut and mounted directly without further staining. From 

 3 to 7 days seems sufficient to decalcify ordinary specimens. The tissues are thor- 

 oughly blackened, but the nerves most intensely so (except the fat), so that they 

 can in sections easily be followed peripherally. The tissue, however, is so ex- 

 ceedingly brittle that I found it impossible after repeated trials to get satisfac- 

 tory serial sections. Furthermore the penetrating power of the fluid is so slight 

 that only the outer parts of the specimen are properly fixed. The brain, even 

 when directly exposed by slicing off" nearly half of the head, is always in a very 

 bad state of preservation. Peripherally, however, the fixation of the medullate d 

 nerves is the most perfect that I have ever been able to secure by any method, 

 and the imperfect series which I have prepared by this method have been of 

 the greatest use to me, especially when controlled by proper Weigert prepara- 

 tions for the internal courses of the nerves. 



B. — Flemming's Fluid. 



Flemming's second, or stronger formula alone has been employed. 

 This reagent requires a rather longer time for decalcification than Her- 

 mann's fluid, from one to three weeks with frequent renewal being re- 

 quired for the head of a minnow. At the end of that time the tissue 

 is, of course, exceedingly friable, but with very careful handling will 

 hold together sufficiently to cut well and gives perfect serial sections. 

 The fixation is all that could be desired for general purposes and the 

 medullary sheaths are well preserved both centrally and peripherally. 

 The smallest fibers are, however, not quite so well fixed as by Her- 

 mann's fluid. In the deeper parts of the specimen they often lose the 

 sharpness of their contours and gelatinize more or less, probably under 

 the influence of the other acids before the osmic acid has sufficiently 

 permeated. The coarse-fibered components are always perfectly pre- 

 served even in the interior of the brain. The peripheral tissues are 

 blackened somewhat but not so much as by Hermann's fluid. I had 

 hoped to be able to mount the sections directly after this fixation with- 

 out further staining, relying on the osmium precipitated in the nerve 

 sheaths to differentiate the fibers, as has been done by others with am- 

 phibian and selachian material and as I have done with the bony fishes 

 after fixation with Hermann's fluid. Curiously enough, however, the 

 nerve fibers though well fixed, and that too evidently with the osmic 

 acid, are not at all discolored, but upon dissection the nerves stand out 

 as white cords among the blackened muscles, etc. 



40 F. The entire head of a small adult (about 6 cm. long) was fixed for 

 six days in Flemming's fluid. Though the decalcification was not quite com- 

 plete, yet a series of sections was obtained and stained with the usual Haiden- 

 hain iron-hjematoxylin (mordant in iron alum, stain in aqueous ha:matoxylia 



