THE DOUBLE REFRACTION OF CHITIN

The double refraction of the chitinous hair of the crayfish is positive with respect to the axis of the hair, and is largely caused by the arrangement of submicroscopic, elongated chitin particles parallel to this axis (form birefringence). Using a series of relatively unreactive liquids and fluid mixtures which permeate the chitin framework, the type of curve relating double refraction and refractive index of the imbibed fluid is found to depend greatly on the chemical nature of the fluid. Either a positive or a negative residual birefringence may be found, depending on the choice of imbibing liquid. Separation of form and crystalline elements in double refraction by means of Ambronn''s imbibition technique is therefore unsafe in a system like chitin, where some type of oriented association of the imbibed molecules with the chitin framework is prevalent.     

HISTOLOGICAL STAINING OF LIPIDS FOR THE LIGHT AND ELECTRON MICROSCOPE

1. It is generally agreed that the blackening of osmium tetroxide by unsaturated lipid is too unpredictable to demonstrate lipid in tissues.
2. At neutral pH osmium tetroxide combines with the double bonds in the lipoproteins of cellular membranes (mitochondria, etc.) and the deep colour reaction of ethyl gallate with this osmium provides good staining of lipid for the light microscope.
3. Osmium taken up by tissue proteins at neutral pH is only a small fraction of that taken up by the lipid. (After acid fixatives osmium tetroxide is a general protein stain.)
4. The uptake of Sudan black B by partition from dilute solution is a specific test for lipid, but in normally fixed tissue most of the structural lipid is 'bound' and is not accessible to the dye.
5. Cautious treatment of fixed tissue with dilute sodium hypochlorite will unmask this lipid for viewing by the light microscope.
6. Direct fixation with neutral osmium tetroxide is an effective method for visualizing lipid for the electron microscope (as in the ethyl gallate method for the light microscope). But the poor penetration of osmium limits its use in this way.
7. After formol/glutaraldehyde fixation much of the lipid in the tissues is 'bound' and does not take up osmium. It can be unmasked by a saturated aqueous solution of thymol.
8. The unmasked lipid can then be rendered more osmiophil by partition in a solution of the highly unsaturated terpene farnesol, thus increasing the uptake of osmium in a renewed application.
9. Some of the novel observations on tissue lipids made by these methods are reviewed.     

原生质体扫描电镜观察研究方法的改进及其效果初报

本文介绍了一种原生质体扫描电镜观察研究方法。比较了三种不同配方的固定剂,结果证明;用添加甘露醇作渗透压稳定剂和用原生质体培养液作稀释剂配制的固定剂效果良好。用常规电镜固定剂则会造成原生质体变形、破裂。设计了室温下的快速脱水方案,取得较满意结果。观察到原生质体表面有许多大小约100—200毫微米的微孔结构。