376 H. N, MOSELEY. 



acid, where it sliould be allowed to remain for about a fort- 

 night, the acid being changed every three days. By this 

 time the bony tissue will have become quite softened. My 

 friend Mr. C. Tomes suggested to me some time ago that this 

 softening property of chromic acid was probably due to the 

 sulj)huric acid which, being used in the preparation of 

 chromic acid, is ordinarily present in it as an impurity. Be 

 this as it may, it is much better not to use any other acid, 

 such as hydrochloric, to soften bone for histological purposes 

 generally, but to trust to chromic acid solutions alone, and 

 this is especially the case with Corti's organ. 



The softened cochlea, on being taken from the chromic 

 acid solution, should be placed for a few hours in ordinary 

 and then in absolute alcohol. To prepare sections transverse 

 to the long axis of the spire, it may then be imbedded in the 

 usual manner in^ mixture of sweet oil and wax, which I 

 consider far preferable to paraffin. Sections can be easily 

 made with a sharp razor^ wetted with absolute alcohol, floated 

 off the blade on to a slide stained Avith a simple Avatery solu- 

 tion of carminate of ainmonium washed Avitli absolute alcohol 

 treated with oil of cloves, and mounted m Dammar varnish 

 or Canada balsam, used, of course, cold. 



Sections such as these are very instructive, as, owing to 

 the spiral stru.cture of the cochlea, the lamina spiralis and 

 its appendages are exposed, cut through at various depths in 

 different parts of the same section. Thus in one part may 

 be studied the denuded membrana basilaris, ligamentum 

 spirale, and the bottom of the sulcus spiralis a little further 

 on, whilst the rods of Corti remain in sitii with a section 

 showing the structure of the limbus ; further on still may be 

 seen the superior toothed edge of the limbus and the large 

 heap of rounded cells which lie external to those of Corti and 

 Deiters, and form a prominent ridge on the floor of the scala 

 media of the guinea-pig. 



But in order to thoroughly grasp the anatomy of the 

 cochlea it is necessary to have vertical sections through the 

 central axis of the modiolus. If special precautions be 

 not taken all the membranes, with their attached cells^ 



^ The best razors for fine histological work are, as I have stated before 

 in this Journal, the flexible edged razors made by John Heifor, and 

 stamped " Made for the Army." The hollow ground-out surface of the 

 blade holds plenty of alcohol, which forms a film between the steel and the 

 section, and thus allows the latter to slip along the blade without stickintr. 

 Flat razors are an abomination for such work, though of course, necessary 

 for section instruments. Absolute alcohol should be used for wetting the 

 razor; it does so much more perfectly than weaker spirit, and produces 

 good sections with less trouble. 



