[23] PRESERVATION OF MICROSCOPIC MATERIALS. 629 



for half a minute or more the clove oil is mostly vaporized or driven to 

 the edges of the slide aud around the border of the area which is occu- 

 l^ied by the sections. When this is the case the sections will usually be 

 found to be fixed. Then, before the slide has cooled very much, two or 

 three drops of turpentine are poured upon the sections. The turpentine 

 is warmed by the slide, and the parafiQne from the sections is immedi- 

 ately dissolved away. Turpentine is again dropped on the sections and 

 the slide turned on its edge and drained to wash away all that remains 

 of the parafiine surrounding and included by the sections. Before the 

 turpentine has quite dried upon the slide the mounting is done in Canada 

 balsam dissolved in benzole. The balsam should be thin enough to run 

 readily under a long cover-glass, and under which as many as one hun- 

 dred and fifty sections may be mounted without getting any air bubbles 

 included. 



Such serial preparations enable the embryological investigator to 

 study the morphology of embryos or small objects Avith the greatest ease 

 and certainty, because none of the viscera or organs of even the smallest 

 embryos are displaced or shoved out of their normal positions to the 

 slightest degree in the sections if the object has been properly embedded 

 and the process of mounting conducted with the i>roper care. 



It was my intention at first to give the formulae for the i)reparation 

 and use of the most approved staining fluids, but the recipes for com- 

 pounding these are accessible in a number of hand-books on microscop- 

 ical technology, while Mr. Whitman has already given a very full ac- 

 count of those used with the best success in the zoological station at 

 Naples, in his pajier on methods, from which I have already drawn so 

 largely, the title and place of publication of which I have given in the 

 first portion of this paper. Those staining reagents which are given 

 here are mostly such as are used in combination with some killing or 

 preservative agent. 



The principal object of this paper is to aftbrd directions to collectors 

 desiring to preserve the embryos of the lower vertebrates, fishes, and 

 amphibians in such a condition as will enable the investigator to use 

 them in his researches. As ordinarily preserved in alcohol such objects 

 are next to worthless, either for figuring or dissection, as well as totally 

 useless for microscopic preparations. 



