CHAPTER XXVI. 315 



The Iron-Hcematein Lakes of Benda and M. Heidenhain give good 

 plasma stains, according to the degree of extraction, and would be 

 inferior to none were it not that they stain in the same tone as the 

 chromatin. See also Ehrlich's tri-acid, and his acidophilous mixture, 

 also gold chloride, Apathy's process, 371, and Kernschwarz. 



Imperfectly stained plasma structures can often be well brought 

 out by mounting in Euparal instead of balsam. 



671. Centrosomes. These can be stained by some " acid " anilin 

 dyes, better by a " neutral " dye (e.g. Flemming's orange method, 

 or the Ehrlich-Biondi-Heidenhain stain). But by far the best stain 

 is iron-hcematoxylin. 



It is said by Heidenhain that the stain is obtained in a sharper form 

 by combining the hsematoxylin stain with a foregoing stain with Bor- 

 deaux It. He directs (Arch. mik. Anal., xlii, 1894, p. 665) that the 

 sections (sublimate sections were used by him) are to be stained for 

 twenty-four hours or more in " a weak " solution of Bordeaux, until they 

 have attained such an intensity of colour as that " they would just be fit 

 tor microscopic examination with high powers " (1. c., p. 440, note), and 

 that they be then brought into the ferric alum. After mordanting and 

 staining, the hsematoxylin is to be extracted in the iron alum until the 

 chromatin has become entirely or almost entirely colourless. Instead 

 of Bordeaux, " anilin blue " may be used in the same way. 



The images of these objects given by iron-haematoxylin require to 

 be interpreted with special care. Globular or even elongated 

 objects, such as chromosomes, do not always yield up their stain 

 simultaneously and equally throughout their whole depth, but lose 

 it suddenly and entirely in their outer layers, whilst retaining it in 

 its full strength in their deeper layers. It seems that certain 

 erroneous observations that have been published have been due to 

 this deception. 



672. Cell Granules. For the study of the conspicuous " granules," 

 undoubtedly metabolic products, occurring in certain gland-cells 

 and blood- and lymph-corpuscles, and in certain elements belonging 

 to the group of connective tissues, see the sections on " Connective 

 Tissues," " Mitochondria " and " Fat." The most generally 

 employed stains are the mixtures of EHRLICH. 



Intra-vitam staining is useful here. See 208. See also ARNOLD, 

 Anat. Anz., xxi, 1902, p. 417. 



BENDA (Verh. phys. Ges. Berlin, 18991900, Nr. 14, and Verh. 

 Anat. Ges., xv, 1901, p. 172) gives the following method for demon- 

 strating secretion-granules and distinguishing them from other 

 granules : Harden for twenty-four hours in 10 per cent, formalin, 



