488 HISTOLOGY 



Sections or teased preparations must be kept moist during examination. 

 In order to avoid distortion, they are not mounted in water, but in so- 

 called indifferent fluids, such as the lymph, aqueous humor, serous fluids, 

 amniotic fluid, etc. Of the artificial indifferent media, a 0.6 per cent, 

 solution of sodium chloride in distilled water has been found to cause less 

 distortion than the stronger fluids formerly recommended. 



Ringer's Solution. An indifferent fluid which is perhaps more satis- 

 factory than the 0.6 per cent, salt solution is a modification of Ringer's 

 solution adapted to the tissues of warm-blooded animals. It is to be made 

 in large quantities. 



Sodium chloride 90. o 



Potassium chloride 4.2 



Calcium chloride (anhydrous) 2.4 



Potassium bicarbonate 2.0 



Distilled water 10,000. o 



Examination of fresh tissues reveals but little of the fine details of 

 structure. Since the indices of refraction of the different tissue elements 

 have much the same value, outlines are usually dim and there is very little 

 optical differentiation. The method of handling is prone to produce dis- 

 tortion and with many tissues and organs it is difficult to separate their 

 constituent elements. It is generally necessary to employ more complex 

 methods of treatment to gain an adequate idea of the histological details. 



One of the simplest methods is to add one or two drops of i to 5 per cent, 

 acetic acid solution to the fresh preparation. The nuclei then appear more 

 distinctly. Albuminous granules are dissolved, but fat and myelin are not 

 affected. The white fibers of connective tissue swell and disintegrate, 

 leaving the elastic fibers unaffected. 



Nuclei may be rendered distinct by allowing a few drops of stain to act 

 upon the tissue for a few minutes. A i per cent, aqueous solution of methy- 

 lene blue, or a i per cent, solution of methyl green in 20 per cent, alcohol, 

 or the hsematoxylin solutions, may be used. 



ISOLATION. 



Some tissues cannot properly be separated into their elements in the 

 fresh condition, but may be shaken or teased apart after preliminary 

 treatment. The reagents employed in maceration have the property of 

 softening or removing certain constituents of the tissues, at the same time 

 fixing or hardening other elements. Usually the intercellular portions are 

 softened or removed, while the cellular elements undergo fixation. 



Ranvier's Alcohol. This is a mixture of one volume of 95 per cent, alcohol 

 and 2 volumes of distilled water. The cells of small pieces of epithelium 

 (5-10 mm. square) are separable in 24 to 48 hours. They are examined 

 in the same fluid, or washed in water and examined in glycerin. 



