ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 635 



flat vessels at a temperature of 70-80° C, and repeatedly filtered through 

 hard paper. It is repeatedly allowed to cool at room temperature and 

 melted again. Thus treated the paraffin becomes cleaner, and more 

 transparent. This process of preparation is contiiuied, until a large 

 quantity of paraffin, slowly cooled at room temperature, remains quite 

 clear from small white flakes. 



Blocks should be cooled from below upwards over water at 10-20° C. 

 Any minute gas-bubbles then get free exit upwards, and the lower part 

 occupied by the tissue is quite homogeneous. 



(4) staining- and Injecting. 



Rapid Maturation of HsBmatoxylin.* — L. W. Strong recommends 

 the use of freshly prepared silver oxide. One gram of silver nitrate is 

 dissolved in 50 c cm. of distilled water. Dilute sodium hydroxide is 

 added drop by drop until there is no further precipitation of silver 

 oxide. The precipitate is washed repeatedly — about ten times — to 

 remove all alkali, and is then added to h^ematoxylin or to methylen- 

 blue solutions. These may be allowed to stand for two hours, and are 

 then filtered. The staining solutions are now mature. Unna's poly- 

 chrome methylene-blue is rapidly obtained by this means. 



Modification of van Gieson's Stain. -f — 0. Tolker has found that the 

 ordinary van Gieson acid-fuchsin-picric-acid staining method did not 

 give clear pictures of the finer details of the collagen connective-tissue 

 fibres, but that better results were obtained by altering the concentration 

 and the proportions of the constituents of the reagent. He recommends 

 the following : a 1 p.c. solution of picric acid in water, and a 1 p.c. 

 watery acid fuchsin solution are prepared. Sections fixed on albuminized 

 slides are placed for 24 hours in a mixture of 100 c.cm. of the picric 

 acid solution to 0*5-1 c.cm. of the fuchsin solution. Then after rapid 

 washing with acidified water, they are dehydrated and mounted in thick 

 balsam. In such sections the finest connective tissue fibrils are clearly 

 demonstrated. Previous staining with hematoxylin is undesirable. 



Staining Vascular Bundles. ^: — A. C. Hof has applied certain 

 methods of selective staining based on chemical principles to the prepa- 

 ration of botanical microscopic specimens. A section of a twig uf Acer 

 sesculus, or the like stained with acid fuchsin will present a homogeneous 

 red appearance. The application of a reducing agent will, however, dis- 

 charge the red colour, converting the dye into its leucobase over every 

 part of the section except where the tissues have a specific affinity for 

 the dye. Thus the sclerenchymatous bast bundles stained red show 

 clearly on a pale ground. The author gives a list of dyes, arranged in 

 their chemical groups, indicating which are susceptible to the actions of 

 reducing agents. Of various reducing agents mentioned the author 

 prefers sodium hydrosulphite (NaoS204). He then describes in detail 

 selective methods for staining various tissues. As an example, may ])e 



* Zeitschr. wiss. Mikrosk., xxx. (1913) p. 175. 



f Zeitschr. wiss. Mikrosk., xxx. (1913) pp. 185-7. 



X Abhandl. Senckenb. Natur. Gesell., xxxi. (1913) pp. 467-82. 



