154 E. T. NEWTON ON PREPARING A 



washed and laid in spirits of wine. The hyperosmic acid seems to 

 me to be somewhat uncertain in its action, for sometimes the brains 

 remained soft and unstained in the interior, while at other times the 

 hardening and staining was most successful throughout. 



The next point was to cut up the brain in a definite direction into 

 consecutive sections of a known thickness. 



So much has been said in this Club lately about section cutting, 

 that it would only be wearisome to attempt to describe the process 

 fully. It may, however, be mentioned that a microtome was used, 

 in which the screw for raising the object was divided, so as to 

 register a thickness of about the T oVtt °f an inch. The brain was 

 embedded in wax, in the usual manner, and each slice, as it was cut 

 off, was placed directly upon a glass slip in a drop of glycerine, and 

 numbered. When the entire brain had been disposed of in this way, 

 the sections were cleared of the pieces of wax adhering to them, 

 covered with thin glass, and cemented down. 



The sections which appear to me the most instructive are those 

 cut in a direction as nearly as possible parallel to the front of the 

 brain. One brain, cut in this direction, gave me 34 slices, each about 

 the yoVo- of an inch thick, and as no intermediate pieces were lost — 

 although some were subsequently injured in the process of mount- 

 ing — I had the whole of this upper division of the brain in a con- 

 secutive series of slices, and, therefore, in a very satisfactory condi- 

 tion for work. Any one who, in working out structures by means of 

 sections, has endeavoured to trace the various parts through a series 

 of slices, will understand how difficult it is to keep in mind the 

 structures seen in each, so as to picture to himself the form of any 

 part when entire. And still more difficult is it to convey to others the 

 knowledge which one has gained by the examination of such a series. 



Now it seemed to me that, if a drawing of each section of the 

 series were made, and the corresponding portions in each coloured 

 some definite tint, then the structures presented would be much 

 more easily understood, inasmuch as they could all be laid before the 

 eye at one time. I determined, therefore, to prepare such a series 

 of drawings with the camera lucida, and the diagrams numbered 

 2, 4, 6, 10, 13, 17, 20, 25 (Fig. 3), represent the most typical 

 sections of this series ; only one-half of each section being here 

 represented. 



In section No. 2 may be seen, at the lower part, a portion of the 

 antennary lobe (al). In the middle is a mass of nervous matter, 

 here distinguished by vertical lines, and marked (a). Above this is a 



