1888.] MICROSCOPICAL JOURNAL. 205 



Lycopodium. — ' Under the microscope, the granules are seen to be four- 

 sided, reticulated, with short projections on the edges.' There is but little use of 

 examining these granules dry. They can be mixed with glycerin and examined 

 with powers from 125 to 300 diameters. The granules average about 

 twenty-eight micromillimetres (i -900th inch) in diameter. 



Massa Hydrargyri. — ' Continue the trituration until globules of mercury 

 cease to be visible under a lens magnifying ten diameters.' The remarks 

 made about mercury with chalk also apply to blue mass. 



Un^uejittim IIydra7-gyri. — ' Continue the trituration until globules of 

 mercury cease to be visible under a magnifying power often diameters.' This 

 test is too severe for the commercial mercurial ointment. I find that the large 

 globules average about sixty-three micromillimetres (i -400th of an inch) in 

 diameter and are readily seen by aid of the power designated. This forms a 

 very pretty specimen for a power of fifteen or twenty diameters. The globules 

 of mercury settle to the lower side of a slide, so the position should be occa- 

 sionally changed. 



(To be continued.) 



Notes on the Technique of Frozen Anatomical Sections."* 



By D. S. lamb, 



n. S. MEDICAL MUSEUM. 



The part to be frozen should be in precisely the position desired, and free 

 from folds or depressions of the skin. It should be frozen so that all parts, 

 bone, etc., will cut alike. The section should be cut in a cold room, the saw 

 being cold and very sharp. When made, the section will be found to be 

 covered with sawdust. The amount of this will be greater if the freezing be 

 not complete. It has been recommended by some to pour hot water over 

 such a section, then scrape the dust away rapidly and carefully. This is a 

 very delicate part of the process, and its successful performance has much to 

 do with the appearance of the specimens. In my opinion, however, after a 

 great deal of experience with alcoholic specimens, it is best to place the sec- 

 tion at once on a plate of glass, and lay it in a dish of cold alcohol. After 

 the usual hardening, there is then no difficulty in working oft' any loose mat- 

 ter by using a stream of water. It is an advantage to have the vessels injected 

 before freezing. The contrast is greater, and they are shown with greater 

 distinctness. The alcohol used in hardening should be renewed a few times ; 

 the first renewal within a few days, or a week at the most ; the second re- 

 newal will depend on the thickness of the section. For freezing, a low, dry 

 temperature is best ; below zero. But if the box be exposed to a low tem- 

 perature for several days, then a night of + 10° F. may freeze it. A freezing 

 mixture of ice and salt also will do the work. The melted water must, of 

 course, have a chance to run oft'. 



The great advantage of frozen sections is the almost absolute accuracy of 

 relations which are obtained, and not obtainable by any other method. The 

 slight increase in size produced by the freezing is, no doubt, fully balanced 

 by the contraction produced by the cold upon the contractile tissues. While 

 the frozen section is still hard, a plaster cast may be made, and from this 

 another (the reverse), which will resemble the section, and may be colored 

 to life afterwards. Such a cast is very useful for instruction, and has the ad- 

 vantage of preserving at a cost less than that of preserving in alcohol. 



* Read at the 79th meeting of the Washington Microscopical Society, Washington, D. C. 



