22 CUTTING AND MO UNTING TISS UES. 



evaporate until it is of the consistency of the former. After this, 

 it is taken out and arranged in position on a cork or block of wood 

 of convenient size to fit in the jaws of the microtome. By means 

 of a camel's hair brush the material on the cork is covered with 

 successive layers of collodion until it is quite enclosed in the mass. 

 Allow each coat to dry slightly in the air before applying the next. 

 After the tissue is covered it is placed in about 80 per cent, alcohol 

 until hard enough to section. Much difference of opinion exists 

 regarding the proper strength of alcohol to use for hardening the 

 collodion, but 80 per cent, answers very well, and the tissue can be 

 kept in it a long time without deteriorating. After a few hours the 

 collodion will be firm enough for use. Sections of small or deli- 

 cate objects can be cut by allowing them to harden in a block of 

 collodion and then carefully clamping it directly in the jaws of the 

 microtome. For sectioning, any sliding microtome will answer, but 

 one especially adapted for the purpose will enable the object, which 

 can be clearly seen through the collodion, to be inclined in any 

 desired position and sections taken in any plane. It is also neces- 

 sary that the sections be removed with a long sweeping cut, since a 

 direct cross-cut would tear them. The sections should be covered 

 with alcohol while being removed and then floated from the knife to 

 the slide. (See P. A. Fish's modification, Proceedings Am. Mic. 

 Soc. Aug, 1893.) The slower the section is cut, the better it will 

 usually be. Serial sections can be arranged in their proper place on 

 the slide. For fixing to the slide, blow some dry ether vapor on 

 the object (Fig. 3), or add a drop of ether to the side of the prepara- 

 tion. The ether dissolves the collodion and fastens the sections in 

 place. The preparation is then washed with water, stained, the 

 surplus stain washed off with water, the sections dehydrated with 

 95 per cent, alcohol, cleared, and mounted in balsam. 



For clearing, the carbolic acid and turpentine mixture is 

 to be recommended. It clears quickly and does not injure the 

 most delicate tissues. For staining, one must use that which 

 seems best adapted for their purpose, but for general study, 

 haematoxylin seems especially adapted for collodion sections. 



Some difficulty may arise in cutting sections that have in them 

 free parts. It sometimes happens that they become detached from 

 the collodion and float away. In this case, the section can be 



