204 HOW TO WOK 1C 



the microscopical observer. It has the property of dissolving 

 granular matter composed of albuminous material, and causes the 

 cell-wall and many kinds of formed material to become very trans- 

 parent ; although it often renders the nucleus darker and more 

 distinct. In many instances the action of the acid upon the cell-wall 

 is curious ; the formed material becomes more pulpy and thicker, 

 and approaches in tenuity and refracting power the solution in which 

 it is immersed In numerous instances, by adding a saline solution 

 to cells which have been previously rendered transparent by acetic 

 acid, they again contract, and the outline becomes distinct. In 

 some cases, however, the outer part of the cells is actually dis- 

 solved by the acid, and the germinal matter is set free. Acetic acid 

 is> very frequently used to make epithelial structures transparent, in 

 order that the arrangement of the minute vessels and nerves in 

 papilla?, &c., may be demonstrated, as in the case of the tongue, 

 skin, &c. Sections of preparations which have been hardened by 

 maceration in alcohol, may require to be boiled slightly in acetic 

 acid to render them transparent. The action of acetic acid on white 

 fibrous tissue is. very characteristic, as it converts it into a transparent 

 jelly-like mass, in which a few nuclei are visible. Upon the yellow 

 element, on the other hand, this reagent exerts no action what- 

 ever. 



Acetic acid may also be employed for testing crystalline bodies, 

 as phosphates and carbonates. By it phosphate or carbonate of lime 

 may be distinguished from oxalate of lime (all which are insoluble 

 in water), by dissolving the two former, while it does not affect the 

 latter even if boiled with it. The action of acetic acid, upon any 

 particular tissue, upon any form of cells, fibres, &c., that are subjected 

 to examination, should always be specially noted. Many tissues are 

 quite insoluble in acetic acid, though they are not rendered opaque 

 by it. 



Nitric Acid. Strong nitric acid dissolves albuminous substances, 

 but first colours them deep yellow. Dilute nitric acid is much 

 employed in microscopical research. An acid composed of one part 

 of acid to two or three of water, forms a good: solution for hardening 

 some structures previous to cutting thin sections. The thin sections 

 may sometimes be rendered very transparent by being treated after- 

 wards with dilute caustic soda. For demonstrating muscular fibre-cells, 

 nitric acid is a valuable reagent. For this purpose the solution should 

 contain about twenty per cent, of strong acid, and the muscular fibre 

 should be allowed to macerate in it for some days, when small pieces 

 may be removed with scissars, and after being carefully torn up with 

 fine needles, subjected to examination. 



