io6 



HA RD WICKE'S S CIENCE- G OS SIP. 



and if the investing membrane be injured the internal 

 parts are apt to be squeezed out in the hardening 

 process. The fresh brain, cleared from the surround- 

 ing parts, was placed for a few hours (6 or 8) in 

 an aqueous solution of hyperosmic acid (\ to | per 

 cent.) It was then washed and laid in spirits of 

 wine. The hyperosmic acid seems to me to be some- 

 what 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 thick- 

 ness. 



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, how- 

 ever, 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 -^ m 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 instruc- 

 tive 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 thirty-four slices, each 

 about ^ inch thick, and as no intermediate pieces 

 were lost — although some were subsequently in- 

 jured in the process of mounting — I had the whole 

 of this upper division of the brain in a consecutive 

 series of slices, and, therefore, in a very satisfactory 

 condition 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. 93), represent the most typical sec- 

 tions 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 («/). In the middle is 

 a mass of nervous matter, here distinguished by 

 vertical lines, and marked (a). Above this is a cap- 



like portion, distinguished by horizontal lines (c)» 

 These are the portions which should be borne in mind 

 in passing through the series. 



In No. 4 we find that while the parts noticed in 

 No. 2 remain much the same, two dark masses (mb) 

 have appeared in the upper portion, close to the mass 

 (a), but definitely separated from it. 



In No. 6 the dark masses have increased in size 

 and become somewhat curved, but the most obvious 

 difference is that the mass (a) has suddenly extended 

 inwards and downwards to the middle line of the 

 brain (in). 



In No. 10 the dark masses are much more deeply 

 curved, the upper portion of the mass (a) is rather 

 less, and another process has begun to extend upwards 

 and outwards (st). 



In No. 13 the most important point to notice is 

 that, while the inner mass (a) has almost disappeared, 

 the outer one (st) has extended upwards, and may be 

 seen to join the outer dark mass. 



In the 14th section the outer mass (st) joins the 

 inner dark mass also, and this junction extends as far 

 as the 1 8th or 19th section. 



In No. 17 the outer mass (st) may be seen joining 

 both the dark masses, which are here very deeply 

 hollowed out. 



In No. 20 the outer mass has entirely disappeared, 

 and we have simply a small portion of the lower 

 mass (m) left close to the middle line, the dark masses 

 are somewhat smaller. The extension (com) seen just 

 below the antennary lobe is the commencement of the 

 commissure to the lower division of the brain. 



In the sections which follow, all the parts above 

 mentioned, excepting the commissure (com), get 

 gradually less, and the dark ones are seen, for the 

 last time, in section No. 25. The median portion (;«), 

 however, may be traced to the 28th section. 



The next step in the process was this : It occurred 

 to me that, if the card, upon which these outlines 

 were made, were of a thickness proportionate to the 

 enlargement of the drawings, and if each were cut 

 out, and the whole piled together, one ought to have 

 a model of the exterior of the brain. I set to work, 

 therefore, to do this, but in order to lessen the labour 

 as much as possible, it being merely an experiment, 

 it seemed desirable to make one half first, and instead 

 of making models of the whole series, the thickness 

 of each slice was doubled, so that it was only necessary 

 to make seventeen, taking, as a pattern, every alternate 

 drawing. 



The material used was soft pine-wood, each 

 piece being about \ inch in thickness. Having cut 

 out each model slice with a fine saw, the whole 

 were piled together in their relative places and 

 temporarily fixed, so that the corners might be 

 trimmed off, and the result was the form which is 

 seen in the model of one half of the upper brain 

 (fig- 94)- Tne different slices, however, were not left 

 fixed together, but were separated and arranged so 



