332 CYTOLOGICAL METHODS. 



for a few pieces of tissue. Upgrade in alcohol, pass through toluol, 

 embed in wax. The bodies reducing the osmium iodide go black, on a 

 pale grey background. One may subsequently stain in Altmann (mito- 

 chondria red, lyosomes black) or in iron hsematoxylin. It is possible to 

 distinguish between lyosomes and fat, by fixing some of the same tissue 

 in Flemming and comparing the two preparations ; or by comparing 

 the central part of the osmium iodide preparation with the periphery 

 where the fixation is due to the Os0 4 exclusively. 



I have tried this method, at present with disappointing results. 



698. Marine or Fresh Water Organisms ^and Techniques for the 

 Cell Inclusions. If you are going to use a formalin- chrome technique, 

 kill the animals by adding neutral formalin to the water ; if an 

 osmic technique is to follow, kill with Os04 ; wash slightly in aq. 

 dest. in both cases and then transfer to the special fixative. See 

 also under " Protozoa " and " Plankton." 



699. The Centrifuge and Polariscope Microscope in Obgenesis Studies, 

 etc. In examining large differentiated cells, such as ovarian or nerve, 

 most valuable help can be obtained by use of a powerful centrifuge. 

 Tissues or small gonads or whole invertebrates are placed in a tube and 

 centrifuged at high speeds (circa 3,000 revolutions) for from a quarter 

 of an hour to one hour. The centrifuged tissues or animals are imme- 

 diately divided out among several capsules and fixed by several methods 

 which have previously been found to show the various cytoplasm ic 

 inclusions : the specifically stained layers can then be examined. We 

 are of the opinion that no study of the inclusions during cell differentia- 

 tion is complete without recourse to this method. See also GATENBY, 

 Quart Journ. Micr. Sci., 1920 ; LILLIE, Biol. Bull., 19089. 



FAURE-FREMIET (C. E. Soc. Biol., Paris, Ixxxiii) attaches a small 

 platform to the centrifuge, so that preparations on the slide, under 

 coverslip, can be centrifuged and examined from time to time. 



The polariscope microscope has proved very useful, not only for 

 studying the musculature of small animals, but also for discriminating 

 between various fatty and lipoid materials. In working on accumu- 

 lations of masses of metaplastic substances in embryos, or in eggs and 

 other differentiated cells, polarised light is often most helpful. The 

 subject is dealt with in 768 by Cramer. 



700. Vital Staining of the Mitochondria. There is probably no 

 specific intra vitam stain for the mitochondria alone, most of the 

 so-called specific stains will tinge other bodies. E. V. Cowdry has 

 summarised the various methods used for this purpose (Contrib. to 

 Embryol Carneg. Inst., Washington, viii, 1918). 



Four stains (Janus green B, Janus blue, Janus black I, and 

 diethylsafranin) will give an intensely positive reaction on the 

 mitochondria of freshly drawn human lymphocytes. All these are 

 Hoechst proprietary preparations; I find the Janus green of 



