252 



SCIENCE. 



3d. A longitudinal section nearly parallel with 

 the former, running from the anterior prolongation 

 of the olfactory bulb through the middle of each 

 cerebral and optic lobe, and striking the lateral con- 

 voluted mass of the medulla oblongata, could be 

 made from the same brain, as a supplement to the 

 elucidation of the internal contours. 



4th. One horizontal dissection exposing the ven- 

 tricular floors, from above, and another exposing 

 the ventricular roofs from below, will still further 

 clear up these relations. 



5th. A series of transverse sections, taken per- 

 pendicularly to the peduncular axis, will be es- 

 sential to a comprehension of the relations of the 

 ventricles and deeper parts for each altitude. The 

 sections should be taken at distances of from one to 

 three millimetres apart, according to the size of the 

 brain, then preserved in separate bottles and labeled 

 in numerical order. 



All these preparations should be made from 

 brains hardened in absolute alcohol, and the dissec- 

 tions should be made after the brain has been kept 

 thus for one month, if the working season is in 

 summer, and one or two weeks or even a few days, 

 if the season is winter. 



My plan, when engaged in this and similar work, 

 has been to expose the cranial cavity by cutting 

 away the surrounding parts with a strong knife 

 until the brain level is reached. This requires very 

 little practice. Then the lateral walls are broken 

 away with a forceps, or cut away the same knife, 

 and the student may then clear up the tracks of the 

 cranial nerves for a short distance. The brain is 

 not to be removed from the skull base, but left in 

 contact with it, a smooth round head of a needle 

 may be employed to bread up the arachnoid attach- 

 ments there, and facilitate the penetration of alcohol 

 to the basilar parts, but this is all that should be 

 done. The brain must be immersed in alcohol, 

 with the base of the skull in connection therewith, 

 at least by means of the emerging nerve roots, else 

 the topography may become disturbed. 



The membranes (excepting the dura of the con- 

 vexity) should not be touched, for it is desirable to 

 trace their connections with plexiform structures 

 penetrating the fissures and cavities of the encepha- 

 lon, as these may be of service in explaining certain 

 homologies. 



Alcohol is selected as the preserving fluid for the 

 reason that it does not render the specimens too 

 brittle for coarse dissection, which the chromic salts 

 do, nor distorts the contours as does glycerine. 



The transverse sections can be made in a micro- 

 tome, moving the piston the distance of the thick- 

 ness of the required section, before each section is 

 cut. Previous to each cutting, the imbedding 

 matrix should be removed to a little below the level 

 of the section. All other sections can be made 

 without a microtome, it being well, however, to fix 

 the brain in a wax or a paraftine layer, poured on 

 a glass plate. Adherent particles of the material 

 thus used can be subsequently removed with tur- 

 pentine, when the specimen is prepared for perma- 

 nent preservation. It is needless to add that all 

 sections and dissections can be done a hundredfold 

 better under the surface of a fluid like alcohol or 



water, than by simply wetting the knife with these 

 fluids, as text-books direct. 



All the work so far mentioned is only preparatory 

 however. It is merely destined to furnish on the 

 one hand a topographical guide to the more impor- 

 tant work which is to follow, on the other to sup- 

 plement the ascertained relations of ganglionic 

 masses and fascicular tracts by a plastic conception 

 of the encephalic segments which contain them. 

 The work which is to follow is far more tedious, 

 but also far more important; its methods are those 

 employed in studying the microscopic anatomy of 

 embryos. 



For the purposes of microscopic anatomy the 

 brains of smaller species are as preferable, as those 

 of the larger species are desirable for the coarse 

 anatomy. The brain of a sturgeon twelve inches 

 long, will show all the microscopical details as 

 well, and be easier of manipulation than that of one 

 twelve feet long. The latter's had best be devoted 

 to naked eye study. 



If the weather is cold, the animal perfectly fresh, 

 and the specimen can be kept in a temperature near 

 the freezing point (it should never reach or drop 

 below the latter,) the brain can be immediately 

 transferred to a solution of chromic acid of a light 

 sherry color. In my experience this tint, tested in 

 a two ounce graduate, is a far more reliable gauge 

 than any weighing by so many grains to so many 

 ounces, that is ordinarily recommended. After 

 staying a week in this solution, it is transferred to 

 one of bichromate of potash, having the same color. 

 Here it remains, care being taken to have always 

 at least one hundred times as much fluid volume as 

 specimen volume, until the desired degree of hard- 

 ness is attained. The latter is hard to describe in 

 words, but an adequate conception can be best con- 

 veyed by saying that the specimen should be un- 

 yielding to pressure, and yet not altogether inelas- 

 tic. The membranes will now separate readily, 

 and the specimen, first washed in water, is trans- 

 ferred to a neutral (long stood, and repeatedly fil- 

 tered and mouldless) carmine solution, so concen- 

 trated as to appear black in a depth of six inches. 

 Here the specimen is left for from one to three 

 weeks, according to the size of the brain. Then it 

 is again washed, put in water containing two per 

 cent, of glacial acetic acid for twenty-four hours, 

 washed again, transferred to proof spirit for a day, 

 then finally to absolute alcohol, until such time as 

 the observer is ready to make his sections. 



When this time arrives (and it is best not to defer 

 it over a month) the brain stained and hardened as 

 it is, is transferred to clove oil, which penetrates and 

 drives out the alcohol in a few days. The trans- 

 lucency of the specimen is a sign that this has been 

 accomplished. It is then taken oft', the superfluous 

 clove oil drained from the surface, and imbedded in 

 a microtome with paraftine. The superfluous 

 matrix being removed with each section, the cutting 

 is done with turpentine, and each section, stained 

 and transparent, can be transferred to its appropri- 

 ate slide and mounted, so that the order in which 

 each section belongs is preserved. This is an im- 

 portant advantage. 



If the weather is warm, the brain should be sub- 



