8o BASIC METHODS FOR EXPERIMENTS 



to handle. A very beautiful plasma stain is given by Bordeaux 

 red. For details concerning these and other plasma stains, the 

 worker may consult standard text books. I find that Heiden- 

 hain's iron-alum haematoxylin gives clear pictures of the plasma. 

 One can obtain dark blue chromosomes on a beautifully trans- 

 parent, brilliant robin's egg blue plasma background superior to 

 that given by any plasma stain. One needs only to time the 

 duration of the baths in the mordant (4 per cent ferric alum) 

 and in the stain. The diiTerentiation should not be allowed to 

 proceed to the point at which the plasma appears yellow or 

 yellow-white but should be terminated when the plasma is grey. 

 The subsequent washing, dehydration and clearing will give the 

 desired bluish tint to the plasma. If it does not, the tap water 

 should be made slightly alkaline. These results are best 

 obtained after fixation with the modified Meves. However, 

 some of the most brilliant plasma staining with Heidenhain's 

 haematoxylin that I have obtained Is that of cells fixed in Bouin 

 and cleared from 80 per cent, alcohol In aniline oil — a method 

 which years ago I recommended to other workers. For example, 

 Dr. Ezra Allen used it at my suggestion with great success on 

 mammalian cells. Although it is sometimes valuable to use two 

 stains, one for nucleus and one for plasma, for the experimental 

 embryologlst whose primary aim In using sectioned eggs Is to 

 check observations on the living by study of the fixed, I believe 

 that the single staining with Heidenhain's haematoxylin suffices. 

 Stains for mitochondria and Golgi apparatus. — The staining 

 of cell inclusions, as mitochondria and Golgi apparatus, is 

 generally regarded as extremely difficult. I should say that of 

 all structures in cells these prove to be the most exasperating 

 because the results are so varied. Failures are usually attri- 

 buted, as in the case with safranin staining, to the quality of 

 dyes employed. Undoubtedly, this is a factor. Nevertheless, 

 it Is true that two workers using the same dye and following 

 exactly the same procedure, often obtain different results. This 

 Is especially the case with the Benda method for staining 

 mitochondria and to a less degree with Altmann's simpler 

 method. After the Benda method, however, the worker can 

 depend upon perfectly constant results by using the method 

 given above for successful safranin staining, namely, to clear the 



