J. W. GROVES OJST SECTIONS OF ANIMAL TISSUES. 237 



C. Which will stain in 

 the mass and harden J 

 at the same time. 



Osmic Acid. 



Picric Acid. 



Gold Chloride. 



Alcohol + Borax Carmine. 



Alcohol -+- Golding Bird's Logwood. 



Alcohol -f- Eosin. 



With regard to these, I will give some general rules applicable to 

 most, and then proceed to notice each separately. 



In staining, it is a general rule of almost universal application 

 that the fluid should be weak and the quantity large in proportion 

 to the number of sections, or to the mass, as the case may be. 



A section which has been in a fluid so weak that 24 or 48 hours, 

 or even more, have been required to produce the requisite depth of 

 colour is almost always better stained than one which has been in fluid 

 which will produce the same tint in a shorter time, for the following 

 reason : that a fluid commences to stain a tissue directly it comes 

 in contact with it. Now from this it follows that the surfaces of the 

 section are stained much sooner, and consequently more deeply than 

 the intervening portions ; and if the fluid is strong, this difference 

 will be great. 



Again, to produce the best results, the sections should be as thin 

 as possible. 



a. Because they take the stain more perfectly. 



b. Because the thinner they are the less thickness of coloured 

 structures the light has to penetrate before reaching the lenses of 

 the objective ; besides, it enables the deeper structures to be more 

 readily examined with high powers. 



Those colours are preferable which are cool and pleasant to the 

 eye — i.e., those which contain least red and yellow. 



Provided the staining is perfect, and sufficient to show all the 

 detail of which it is capable, the paler it is the better. 



a. Because in the examination with the microscope less light is 

 required, and consequently a continuous protracted observation is 

 less fatiguing to the sight. 



b. The eye is not so immediately attracted by points and streaks 

 of bright colour, thereby running the risk of passing over unnoticed 

 details of structure of equal importance, but which do not obtrude 

 themselves before us with the same glaring pertinacity. 



Finally, it may be remarked that it is better to use distilled in 

 preference to ordinary water in all processes connected with staining. 



