420 MICROSCOPICAL TECHNIQUE. 



vous system originally described by Van Gieson. It is as follows: 

 (i) Stain sections — preferably from tissues hardened in Miiller's 

 fluid — three to five minutes in haematoxylin (Delafield's or ordinary 

 alum haematoxylin) ; wash well. (2) Stain again in a mixture of 

 saturated aqueous solution of picric acid and a saturated 

 aqueous solution of acid fuchsin, sufficient of the latter to 

 make a dark red fluid. (3) Pass rapidly through water, then 

 through spirit, alcohol, and origanum oil ; mount in balsam. V. 

 Kahlden has had good results with this method. Axis-cylinders 

 are stained deep red ; medullary sheaths, yellow ; neuroglia a 

 reddish tint ; nuclei, blue or violet ; sclerosed tissue, an intense 

 red ; hyalin material stains a deep red ; colloid, a fainter red or 

 even slightly brown. The relation of amyloid material, which 

 stains a light red to the tissue constituents, especially the vessel 

 walls, is brought out better by this than by any other method. 



Preparing and examining Sections of Scales of Lepidosteus.* 



Mr. W. S. Nickerson, in his interesting paper on the development 

 of the scales of Lepidosteus, gives the following method for pre- 

 paring the sections : — "In all, except very young stages, it was neces- 

 sary to decalcify the material before it could be sectioned, and, even 

 after decalcification, sections in most cases could not be cut thinner 

 than 15 micromillimetres, and after, in the later stages, it was neces- 

 sary to make them 20 and 30 micromillimetres thick. For decalci- 

 fying, I used 90 per cent, alcohol, to which was added a small quan- 

 tity of 10 per cent, hydrochloric acid (in the ratio of about 3 to i). 

 The tissue was usually left in this acid alcohol 24 hours or more, and 

 then soaked in several changes of fresh alcohol to remove all traces 

 of the acid before staining. Sections prepared by grinding down 

 scales have also been studied, as well as scales freed from the soft 

 tissues by treatment with caustic potash. Only by the use of the 

 latter re-agent was I able to get a satisfactory knowledge of the 

 spines which cover the scale in its immature state. The stains 

 which have given the best results are Boehmer's alum haematoxylin 

 and Kleinenberg's haematoxylin. As a nuclear stain the former is 

 much the better ; the latter is especially useful in the study of the 

 glands of the epidermis, and in bringing cell-membranes into pro- 



*Bull. Mus. Comp. ZooL, Harvard College, xxv. (1893), pp. 117 — 1193. 



