The anatomy of the central nervous organs in health and in disease / by Heinrich Obersteiner ; translated, with annotations and additions, from the third German edition, with all the alterations and corrections prepared by the author for the forthcoming fourth German edition by Alex Hill.
- Heinrich Obersteiner
- Date:
- 1900
Licence: In copyright
Credit: The anatomy of the central nervous organs in health and in disease / by Heinrich Obersteiner ; translated, with annotations and additions, from the third German edition, with all the alterations and corrections prepared by the author for the forthcoming fourth German edition by Alex Hill. Source: Wellcome Collection.
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![SECTIONS. transparent sections presents no little difficulty, and the conception of structure which we gain by this method needs to be checked by seeing the object itself as exposed by dissection. When such a series is to be made, the central nervous system must first be hardened. Attempts to freeze the tissue and cut it when fresh have not been successful, for the natural brain-substance suffers too much in the pro- cess, and the preparations thus obtained are unsatisfactory. The freezing method is, however, useful for tumours. We are obliged to have recourse to hardening fluids, and amongst them solutions of chromic salts stand first, and are to be preferred to simple chromic acid. Bichromate of potassium is most used. Fresh pieces of the central nervous system arc placed in as large .a vessel as can be had, filled with a 1 per cent, solution of this wilt. The fluid is repeatedly changed for the first few days, and is rendered gradually stronger, until it is brought up to 2 or 3 per cent., at which strength the pieces arc left until they arc sufficiently hard. The time needed averages six to eight weeks, but depends on various circum- stances, on the temperature of the room for example (it requires less time in summer than in winter); small pieces, too, take a shorter time than large ones. In an incubator, in which the temperature is maintained at from 35° to 40° C., it is possible to harden the tissue sufficiently for cutting in from eight days to a fortnight. The hardening is hastened by adding to the bichromate of potassium a little free chromic acid (20 or 30 drops of a 1 per cent, solution of chromic acid to 500 grms. of the bichromate solution). Under the influence of a constant current of electricity, emanating from the positive pole, the hardening is said to proceed with extreme rapidity, sections of the spinal cord being ready in four or five days (Minot•). Treatment with chrome-salts should be carried out in the dark. The time required depends upon the particular part of the central nervous system under treatment. The hardening of spinal cord in chrome-salts requires especial care. After the preparations are ready for cutting, they can still remain for some months in the chromic solution without injury; if they are to be preserved still longer, and if the use of alcohol is to be avoided, they must be transferred to a weak solution (0'5 per cent.) of the salt, in which they can be kept for years. The formation of mould is no sign that the preparations are spoilt. The addition of a little carbolic acid does not prevent the formation of fungi, but checks their growth. Even though the pieces are thoroughly hardened in chrome-salts they can still bear the subsequent hardening in alcohol. This is accomplished usually by washing them out first for several days in water [it is not, as a rule, however, advisable to place them directly in water, but to transfer them from the solution of chromates to 25 or 30 per cent, spirit, which is changed every day until the liquor drawn off is almost colourless], and then for a like time in 50 per cent, alcohol, after which they arc trans- ferred to strong (95 per cent, or, in some cases, absolute) alcohol. To prevent precipitation it is recommended that the vessels should be kept](https://iiif.wellcomecollection.org/image/b28716826_0035.jp2/full/800%2C/0/default.jpg)
