Spinal Cord for Microscopical Examination. 31 



Before being mounted, however, they require to be clarified, 

 or, in other words, rendered transparent, which is done by 

 means of creosote or oil of cloves, or oil of turpentine. The 

 oil of cloves is the best clarifijing medium. Before using the 

 oil of cloves or other clarifying media, all water must be removed 

 from the sections. This is done by immersing them in absolute 

 alcohol. Place the sections in a watch-glass containing absolute 

 alcohol, in order thoroughly to get rid of all water. Then place a 

 . section on a slide, and incline it to one side so as to drain off the 

 alcohol. Allow the section to become sodden but not too dry, then 

 insinuate a drop of clove oil, by means of a small sable-hair brush 

 under the section. (Sable being stiifer than camel hair, is prefer- 

 able for this purpose.) Care must be taken not to aUow any of the 

 oil of cloves to run over the upper surface of the section at first, 

 till all the absolute alcohol has been driven off into the air. 



If the oil of cloves has gone over the upper surface of the pre- 

 paration before the moisture (driven off by the absolute alcohol) 

 has disappeared, you have a cloudiness in your preparation on 

 mounting it in the dammar. When all the moisture, therefore, 

 has been driven off, a drop of oil of cloves is placed on the upper 

 surface of the preparation, and it is examined with a low power often, 

 to see if it has become perfectly transparent. You then soak up 

 the superfluous oil of cloves with hihulous paper, or, if there is no 

 danger of injuring the preparation, transfer it to another slide on 

 which is placed a drop of dammar or Canada balsam (dried and 

 dissolved in benzole or turpentine), and place the covering glass on 

 the preparation. To keep the covering glass in its place until the 

 dammar has dried, a spring chp may be used. 



I may now be permitted to give you a resume of this compli- 

 cated process. 



First, then, the tissue is placed in methylated spirit, then in 

 the hardening fluids, — chromic acid in the case of the cord, — 

 chromic acid and bichromate of potassium in the case of the cere- 

 brum and cerebellum. When hard enough, sections are cut (the 

 razor being wetted with spirit), placed for half an hour at least in 

 potassium bichromate, washed with water, transferred to Dr. Beale's 

 carmine fluid diluted seven times with water. When stained 

 enough, washed with water, and spirit added, in which they are 

 kept till mounted by means of absolute alcohol, oil of cloves, and 

 dammar. The sections must always be manipulated with camel- 

 hair brushes. 



I now come to the Second Division of my subject, namely, the 

 preparation of the brain and cord when hardening fluids are not 

 used. 



The brain, in pieces the size of a pea, when fresh may be 

 placed at once in Dr. Beale's carmine fluid diluted seven times ; when 



VOL. X. D 



