158 Proceedings of the Royal Society of Edinburgh. [Sess. 
the ovary fixed in situ, then removed later for dehydration and embedding. 
This method was found most satisfactory, as in the fresh state the organs are 
difficult to isolate and remove. Some very early pig embryos were sectioned 
in toto to show the genital ridge. I have found, in common with many 
other investigators, that the ovary, more especially that from the human 
foetus, is an extremely difficult tissue to fix satisfactorily, and many methods 
were tried before a fixing solution was found which gave good results. The 
fluids used were Flemming’s solution, Gilson’s fluid, formalin 10 per cent., 
but the best results were obtained by using picro-formalin.* The length 
of time of immersion of the tissue varied according to the age of the 
embryo, very young tissue requiring only half to one hour; for older 
tissue six to twelve hours. The only difficulty in the method is the wash- 
ing out of the picric acid by 50 per cent, alcohol. The sections were stained 
by Heidenhain’s iron-hsematoxylin method, but latterly I have used the 
Weigert rapid method. By the Weigert modification there is no time lost 
in mordanting the sections. The hsematoxylin is made up in two stock 
solutions : — 
Solution A. Hsematoxylin 
Alcohol 96 per cent. . 
Solution B. Ferri sesquichlorate . 
Official hydrochloric acid 
Water 
1 grm. 
100 c.c. 
4 c.c. 
1 „ 
95 „ 
When required for use mix equal parts of A and B ; precipitation ensues, 
and the mixture becomes quite black. The mixture must be freshly pre- 
pared, but can be used as long as no strong odour of ether is present (one to 
more days). Stain the sections for a few seconds, wash in water, counter- 
stain in acid fuchsin picric acid f solution for a few seconds, wash rapidly 
in water, dehydrate in 90 per cent, alcohol, and clear in carbol-xylol, mount- 
ing in Canada balsam. 
B. Ovary of Pig Embryo. 
Embryo 6 cm. in length. The ovary consists of an elongated narrow 
body with a pedicle or stalk. Under the microscope there is not much 
differentiation of structure of medullary or cortical zones. Through the 
* Picro-formalin solution (Bouin) — 
Sat. sol. Picric acid . . . . 75 parts 
Formol . . . . . . 25 „ 
Acetic acid . . . . . 5 „ 
+ To 100 parts of an aq. sol. of picric acid, add 10 parts of 10 per cent. aq. sol. of acid 
fuchsin. 
