1 8 NORMAL HISTOLOGY. 



them more or less opaque, or at least translucent. 

 Now glycerin has the power of penetrating many 

 such tissues ; and since, as a rule, its index of refrac- 

 tion is much more nearly like that of the albuminous 

 particles than is the refractive index of the substance 

 lying between them, when the tissue becomes soaked 

 with glycerin the light passes more directly through, 

 and the tissue is more transparent. Many specimens, 

 furthermore, preserve their structural features very 

 perfectly for a long time in glycerin. 



The stained specimens are either soaked until 

 they become transparent in a small dish of glycerin, 

 and then transferred to a slide and mounted in the 

 same ; or they may be mounted at once, without the 

 preliminary soaking. Eosin is soluble in glycerin, 

 so that if a tissue stained in it is mounted in pure 

 glycerin it gradually fades. To prevent this, the 

 glycerin used for mounting should be slightly tinged 

 beforehand with eosin. 



The strong refractive power of glycerin, although 

 of value in rendering tissues transparent, is, how- 

 ever, in some cases prejudicial to our aims, because 

 it makes them too transparent ; its refractive power 

 being so nearly like that of the tissue elements 

 themselves that their more minute structure is con- 

 cealed. For we find, within certain limits, that the 

 greater the difference between the refractive power 

 of an object and that of the fluid in which it lies, 

 the more distinct will be the outlines of the object. 



