ZOOLOaY AND BOTANY, MICROSCOPY, ETC. 541 



In good sections prepared by either of the first two methods a 

 suspicion of the existence of continuity will be created by the 

 appearance of the cell-contents. A mere suspicion, however, is not 

 sufficient, and to be convinced that it actually exists the ends of the 

 cells must be more closely investigated. For this purpose sections 

 prepared by the third method must be made use of, and even these 

 must be supplemented by others of a still more demonstrative 

 character. The latter may be obtained by slightly modifying the 

 modes of treatment as follows : — 



1st. Sections that are to be treated by the second method should 

 be previously placed for a few moments in a weak solution of ordinary 

 bleaching powder. 



2nd. Sections that have been treated by the third method should 

 be warmed gently in a mixture of equal parts of glycerin and potash 

 solution, before being mounted in glycerin and ammonia. 



Tolu instead of Chloroform for Imbedding in Paraffin.*— Dr. 

 M. Holl finds that objects imbedded in paraffin can be better and more 

 easily cut when they have been previously treated with tolu instead 

 of chloroform. After the object has been hardened in alcohol it is 

 placed directly into the tolu for twenty-four hours (or less for small 

 objects), and transferred from it to the paraffin bath, in which it is 

 also kept for twenty-four hours. 



Imbedding Small Objects.f — For imbedding small objects, e.g. 

 embryos or parts of them, Dr. L. Gerlach gives the following 

 receipt : — 40 grm. gelatin are added to 200 c.cm. of a saturated solu- 

 tion of arsenious acid, with 120 cc. of glycerin. This fluid is clarified 

 with white of egg, and remains perfectly clear for years in a well- 

 stoppered bottle. Objects hardened in alcohol are most suited for 

 imbedding in this mass. They are, prior to imbedding, placed in 

 weak glycerin (glycerin 1 part, water 2 parts), to which some thymol 

 has been added, for two hours or more, according to their size. So 

 as to remove all traces of alcohol, the fluid is changed from hour to 

 hour. 



Advantages and Disadvantages of Different iForms of Micro- 

 tome.t — Dr. M. Gottschau has a useful summary of the advantages 

 and disadvantages of different microtomes. 



Microtomes are referable to two types. In one (e. g. Oschatz's) 

 the object is raised by a micrometer screw, in the other (e. g. Rivet's) 

 by altering its position on a plane which gradually rises towards the 

 horizontal cutting edge of the knife. In the former a free application 

 of the knife in any direction is feasible ; but where the object is slid 

 on a rising rail, the knife must be fastened and guided on a horizontal 

 slide. In the former, again, the preparation must be so firmly clamped 

 or imbedded that it rises without lateral displacement. It is raised 

 by the screw to the fraction of a mm. above the upper opening of the 



* Zool. Anzeig., viii. (1885) pp. 223-4. 



t Grerlach, L., Beitrage z. Morphol u. Morphogenie. Uaters a. d. Anat. Inst. 

 Erlangen, i., Stuttgart, 1884. 



% Zeitschr. f. Wiss. Mikr., i. (1884) pp. 327-48. 



