INJECTING. 399 



out. Then they are dehydrated in 96 per cent, alcohol, and 

 transferred to a clearing fluid (e. y., carbol-xylol (1 part of car- 

 bolic acid; 3 parts of xylol), creosote, bergamot oil, oil of 

 cloves, etc.). The most generally useful clearing fluid is creo- 

 sote. Carbol-xylol cannot be used with sections stained in 

 anilin dyes. Sections are left in the clearing fluid for about 

 five minutes, until they have become transparent. If they 

 remain opaque in places, they have not been entirely dehy- 

 drated, and should be returned to the alcohol. From the clear- 

 ing fluid the sections are lifted on to a slide by means of a sec- 

 tion-lifter or spatula. The excess of clearing fluid is drained 

 off, or, in the case of creosote, removed with a blotting-paper. 

 A drop of Canada balsam is added, and a clean cover glass 

 placed over each section. This is left until the balsam is 

 hardened. 



In some cases it is of advantage to mount celloidin sections 

 in glycerin. For this, it is not necessary to pass the sections 

 through alcohol. The glycerin, which is added to sections 

 placed directly on the slide from water, does not dry. In order 

 to make the specimen permanent, therefore, it is necessary to 

 put a rim of cement around the edge of the cover glass. For 

 this purpose, a mixture is made of 2 parts of paraffin and 8 

 parts of colophonium, which are melted carefully. This is 

 placed around the cover glass and dried by means of a hot 

 wire or needle. 



(h) Injecting. 



This is an art which is learned better through practice than 

 by means of descriptions. It is necessary to use organs from 

 animals which are freshly killed. Certain injection fluids or 

 masses colored with various pigments must be prepared ; and 

 an apparatus must be arranged to supply a constant pressure. 

 This apparatus is connected by means of a system of tubing 

 with a cannula which is inserted in the blood-vessel or duct 

 which is to be injected. The injection fluid is forced in this 

 way into the vessels. 



Certain general points in connection with 'injecting may be 



