MS 34.0 



METAL STAINS 



601 



mounted in cedar oil. This type of mount- 

 ing is necessary, since it is a peculiarity of 

 this technique that sections prepared by 

 it may not be mounted under the surface 

 of a coverslip or they will bleach within 

 an interval varying from a few months to 

 a year; whereas if they are merely var- 

 nished to a shde they may be preserved 

 indefinitely. In the present instance they 

 may be dehydrated in absolute alcohol, as 

 it docs not matter whether or not the 

 celloidin is dissolved from the section. If 

 one is deahng with brittle material or 

 with material for which the celloidin forms 

 the cliief support, it is essential to com- 

 ])lete the dehydration in some alcohol in 

 which celloidin is not soluble. Golgi him- 

 self recommended guaiacol. Whatever me- 

 dium is used for dehydration, clearing 

 sliould always be carried out in cedar oil. 



When it is required to make a more 

 permanent preparation of an individual 

 mount, it is simplest to take it from the 

 thin cedar oil, lay it on a slide, blot the 

 cedar oil from it with the finest filter 

 paper available, and place over the surface 

 a layer of the kind of thickened cedar oil 

 once sold for use with oil immersion objec- 

 tives and still obtainable from some sup- 

 pliers as "cedar oil (special for micro- 

 scopy)." This oil hardens in about 48 

 hours. Two layers will give enough pro- 

 tection, and the only objection to this 

 method of mounting is the tendency of 

 dust to accumulate on the surface. When 

 this has happened to the extent that ex- 

 amination of the specimens is becoming 

 difficult, it is only necessary to wash off 

 the cedar oil with absolute alcohol an'd 

 replace it with fresh cedar oil. Such drastic 

 treatment may not even be necessary, and 

 it is often possible to remove the dust with 

 a cloth moistened in cedar oil. 



Those who are not prepared to indulge 

 in the many experimental processes men- 

 tioned in this technique are recommended 

 to the technique of Golgi 1880 which is 

 universally known as "Golgi's quick 

 process." This involves osmic-dichromate 

 fixation and the entire operation may be 

 concluded in as little as three or four days. 

 It does not, liowever, j^ield results so 

 beautiful, nor is it always i)()ssil)le to se- 

 cure results at all. The advantage of the 



present slow method is that, since numer- 

 ous blocks are removed at intervals, one 

 is certain to find at least one which has the 

 correct degree of impregnation. 



Demonstration of the structure of 



the superior cervical ganglion by 



the method of Kolossow 1896 



This is an interesting mixed silver-osmic 

 method which is ideally suited for the 

 demonstration of nerve fibers in cells 

 within sympathetic ganglia, a subject 

 most difficult to impregnate by other silver 

 techniques. Only two solutions are re- 

 quired. The first is Kolossow's 1897 osmic- 

 dichromate fixative (see in Chapter 18, 

 F 1700.0000 Kolossow 1897) and the 

 second, the silver-osmic stain of Kolossow 

 (see MS 34.1 Kolossow 1897), which is 

 prepared by adding to 250 milliliters of 

 triple-distilled water, first five grams of 

 silver nitrate and then, when this has been 

 completely dissolved, one gram of osmic 

 acid. 



The easiest material on which to become 

 acquainted with this technique is the an- 

 terior (or superior) sympathetic cervical 

 ganghon of a rabbit. Before commencing 

 the dissection of the rabbit it is as well to 

 prepare an adequate supply of the fixative 

 solution and to store this in a chemically 

 clean glass-stoppered bottle. A rabbit is 

 then killed and tied, ventral side upper- 

 most, on a dissecting board. A loop of cord 

 is passed around the anterior region of the 

 head, which is drawn over the edge of the 

 board so as to stretch the neck as far as 

 possible. The neck is then skinned and the 

 superficial fascia removed, the muscles 

 being pulled laterally away from the tra- 

 chea. If this is done in about the central 

 region of the neck, two nerves will im- 

 mediately become apparent. The smaller 

 of these is the descending ramus of the 

 hypoglossal and the larger is the fused 

 tenth nerve and sympathetic nerve from 

 the ganglion sought. This larger nerve is 

 then followed forward by parting the 

 fascia of the muscle to a region just behind 

 the tympanic bulla. Here it will be found 

 to split into two, each of the two smaller 

 tributaries swelling, after a distance of 

 about one half inch, into a ganglion. The 



