THE DISSOCIATION OF TISSUES 721 



Some histologists regard a 0.6 per cent, solution preferable. Normal 

 salt solution has become quite generally displaced by Ringer's Solution, 

 which corresponds more nearly to blood plasma and is less likely to 

 produce distortion. This is prepared, adjusted to tissues of warm- 

 blooded animals, according to the following formula : 



Sodium chlorid 90.0 



Potassium chlorid 4.2 



Calcium chlorid (anhydrous) 2.4 



Potassium bicarbonate 2.0 



Distilled water 10000.0 



In order to render the nuclei more conspicuous a drop of a 5 per 

 cent, aqueous solution of acetic acid may be added. This, however, will 

 dissolve the o collagenous fibers and albuminous granules. The nuclei 

 may be stained by the addition of a drop of a 1 per cent, aqueous solu- 

 tion of methylene blue. 



A 40 per cent, solution of glycerin in distilled water also is useful 

 as an examining medium; better still, the tissues may be suspended 

 in a mixture of equal parts of 95 per cent, alcohol, glycerin, and dis- 

 tilled water. This mixture is especially useful, for in it tissues may be 

 kept for a long period without deterioration. 



Amniotic fluid obtained from pig fetuses is also valuable as a medium 

 for the examination of fresh tissues. 



Hogan (Jour. Amer. Med. Assoc., 64, 9, 1915) has devised a normal- 

 salt-gelatin mixture with a colloidal constitution like that of blood serum, 

 which serves as a favorable indifferent medium for the examination 

 of fresh blood and other delicate tissues. For the method of preparation 

 reference should be made to the original article. 



THE DISSOCIATION OF TISSUES 



It is frequently desirable to dissociate tissues to a certain extent into 

 their component elements prior to microscopical examination. This is 

 accomplished by teasing, or by the solvent action of relatively strong 

 acids or alkalies. Isolation by the latter method is known as maceration. 



For teasing, minute fragments of tissue are separated by the aid of 

 needles or scissors and placed on a clean slide, where they are to be 

 kept always moistened with normal saline solution or other isotonic 



