METHOD OF EXAMINING MORBID STRUCTURES, ETC. 457 



one of the sides of the cover, when it will gradually insinuate 

 itself between the glasses, and act slowly on what is contained 

 there ; in other cases, the cover may be lifted up, and a small 

 quantity of the re-agent added, and the cover quickly replaced, 

 care being always taken that no foreign matters gain entrance 

 into the fluid from without. In the case of blood, the fluids 

 that require to be added are generally ordinary water, serum, 

 and sugar or salt dissolved in water ; but in the case of pus 

 and mucus, which approach each other so closely in many of 

 their characters, it becomes of great importance to have some 

 test whereby they may be distinguished one from the other ; 

 the fluid employed for this purpose is acetic acid ; when this 

 is added to a fluid where pus is present, the globules swell up, 

 and several large transparent nuclei make their appearance ; 

 but when the same acid is added to a fluid where mucus is 

 present, the globules enlarge and show their nuclei, but not 

 so plainly as the pus ; and the liquid termed liquor muci, in 

 which the globules float, is instantly coagulated into a semi- 

 opaque corrugated membrane. The presence of fatty matter 

 is ascertained by sulphuric ether, which readily dissolves the 

 oily part, and if it be contained in cells, as in adipose tissue, 

 the cell walls remain untouched. Earthy matters require the 

 aid of the acids for their solution ; these should not be added 

 in too concentrated a form, in order that their solvent action 

 may be the more easily witnessed. Solid parts, such as 

 tumours, that are to be examined as transparent objects, with 

 high powers, require for the purpose to be cut into exceed- 

 ingly thin slices, and separated, if necessary, by the needle- 

 points ; the sections are to be placed upon a glass slide, and a 

 little serum, or, in the absence of it, white of egg, in water, 

 should be added, in order to float out certain of the parts, and 

 to lessen the refraction of the light at the edges of the object ; 

 water will answer the purpose for some of the hard tissues, 

 but where nucleated or other cells and nervous matter are 

 present, its use is inadmissible, as it is so liable to alter the 

 true appearance of these structures. The sections may be 

 made with a razor or scalpel; for solid organs, such as the 

 liver and kidney, Valentin's knife, described and figured at 



