1 1 MttftTi'dl OIK/ Jfct/HH/N of Examination 



Mftliods of Examination. 



All the normal human and tin- anthropoid brains were hardened in Miiller's fluid or in 

 Orth's solution. a mixture of Miiller's fluid and Formalin; after fixation, orthogonal tracings 

 were drawn, showing the exact disposition of the convolutions and sulei on the various 

 surfaces, and to confirm the correctness of these tracings the same surfaces were photo- 

 graphed. In the case of the anthropoid brains a plaster of Paris cast was always made 1 , 

 and proved of great assistance in facilitating orientation when the preparations were ready 

 for microscopic examination. 



With the hemispheres which were examined completely, the following was the plan of 

 procedure. They were first divided into portions of suitable size for section on the microtome, 

 for this purpose blocks of a length of 5 ctm. were found most convenient: sections of pieces 

 of a greater size are not only difficult to manipulate, but the necessary addition to their 

 thickness impairs their utility as microscopic specimens: furthermore, it is always a distinct 

 advantage to carry the line of cleavage as near as possible at right angles to the main sulci, 

 so that the adjoining convolutions may be viewed in transverse section, an advantage which 

 is sacrificed when very large blocks are taken. Division of the brain so as to give a view 

 of all the principal gyri on transverse section in this manner is not an easy matter, each 

 line of incision has to be carefully thought out and eventually one is left with about 50 blocks 

 for section ; and though labour is multiplied in the preparation of specimens from such 

 a number of pieces the result justifies the expenditure of time, because the discernment and 

 definition of changes in type of structure are facilitated, and also because oblique sections of 

 the convolutions, and especially of the cortex lining sulci, which detract from the value of 

 specimens in a marked degree, are avoided. In the next place, in order that precise 

 orientation and accurate identification of the different sulci and convolutions in the finished 

 sections might be ensured, the lines of cleavage between the blocks were carefully and 

 correctly indicated on the original tracings and photographs. Then the blocks, being numbered, 

 were placed in separate bottles, after- hardened in increasing strengths of alcohol, and imbedded 

 and cut in Celloidin on a Jung Microtome. The sections, of a thickness of 25 /a, were taken 

 at intervals of 1 mm. and preserved in strict serial order between sheets of paper and 

 subsequently mounted and stained ; and so in the case of the central convolutions, for instance, 

 sections were obtained showing their structure at about a hundred different levels. 



As to the method of staining employed, a lengthy experience of processes for the 

 demonstration of cortical nerve fibres has convinced me, that for a faithful display of the 

 more delicate fibrils, a sharp delineation of the larger fibres and the production of a deep 

 coloration of the myelin rendering the specimen alike suitable for drawing purposes and 

 photomicrography, the method known as that of Wolters-Kulschitzky, although a tedious 

 one, stands ahead of all others in the certainty of its results; and this method has accord- 

 ingly been adhered to throughout. 



Then as to nerve cells, one frequently reads statements to the effect that " no attempt 

 was made to examine nerve cells " in such and such a case, " because the brain had been 

 preliminarily hardened in Miiller's chrome solution," but I overcame this difficulty by employing 

 Thionin J c a* my stain. And in spite of the thickness of the sections I was able to 

 see the Nissl bodies clearly, and. what was more important for my purpose, the cell morphology 



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