DR. H. WATNEY ON THE MINUTE ANATOMY OF THE THYMUS. 
1075 
that certain granular cells occur in the blood and in the organs which form the blood ; 
and that the granules in these cells are neither fat nor haemoglobin. 
The Methods used. 
(a) . To tease up the tissue in saline solution, either in the fresh state, or after leaving 
small pieces some hours in yg- per cent, osmic acid ; another method is to immerse 
small portions in a dilute solution of bichromate of potash, to which a considerable 
quantity of watery solution of eosin has been added ; the pieces were usually left in the 
solution from twenty-four to forty-eight hours, at times from one to three weeks ; and 
were then teased in saline solution and mounted. 
( b ) . To make sections of the thymus. For this purpose the tissues were hardened 
in one of the following ways : (1) for ten days in -jt to ^ per cent, chromic acid, and then 
in 50 per cent, alcohol for two days, and afterwards placed in strong methylated alcohol; 
(2) in 2 per cent, bichromate of potash for weeks or months, and then in alcohol; 
( 3 ) in chloride of gold for some hours, and then in chromic acid, and subsequently in 
alcohol; (4) in equal parts of \ per cent, osmic acid, and 3 - per cent, chromic acid, from 
ten to fifteen days, and then transferred to alcohol; (5) in methylated alcohol. 
The sections were, except in a few instances, stained in hsematoxylin, and mounted 
in Canada balsam; some of them were shaken in a test tube, from twenty minutes to 
four or five hours, before being mounted. 
It was found that to shake out the smaller cells, a two rigid hardening of the tissue 
was prejudicial. 
Staining by means of hematoxylin extract. 
It has long been known to those who have used a watery solution of extract of 
hsematoxylin and alum (one part of the extract to three of alum, as recommended by 
Professor Arnold (84) and Dr. Klein (85)) that in certain cases the resulting fluid is 
purple, at other times blue, and occasionally red. The red solution gives a disagreeable 
colour to the sections, and also stains very slowly. 
In working with various microscopical specimens of the thymus, it was found, 
however, that certain tissues were well stained by the red solutions, and others readily 
by the blue. It has been my custom in many cases to double stain the specimens, 
using first a red solution of the colour of Plate 86, fig. 22, c, and deepening the 
staining of the specimen, and making parts of it purple-blue by a solution of the 
colour of Plate 86 , fig. 22, e. 
The method adopted is to leave them in a rather strong solution of c, from sixteen 
to eighteen hours. They are then washed and placed in a weak blue solution, from 
four to twenty-four hours. It is necessary to use the red fluid of such a strength that 
it will not change to blue, even during three or four days’ exposure; and to insure 
this it is better to use it rather strong, as all weak solutions are more liable to turn 
