600 STJMMARY OF CURRENT RESEARCHES RELATING TO 



removed ; it can be covered witli the Canada balsam as easily as if it 

 were under the cover-glass, and without interfering with the security 

 of the cell. The Canada balsam is, of course, best if of such a con- 

 sistence as not easily to become hard and brittle. Professor Hill- 

 house mentions as one of the advantages of this method, that if the 

 section should slip from beneath the cover-glass on the application of 

 pressure, as the thinnest and therefore best sections are apt to do, 

 they would still be visible through the transparent balsam, if its 

 upper surface were made parallel to the slide. It was jocularly 

 suggested at the meeting at which the process was explained that the 

 next step in advance would be to dispense with the cover-glass alto- 

 gether, and encase the object in a layer of glycerine, protected by a 

 horizontal film of balsam. 



Mounting Sections in Series.* — Eeferring to Dr. J. Frenzel's 

 method of mounting,| Mr. E. Threlfall says that it was pointed out 

 to him by Mr. W. H. Caldwell that the use of hot absolute alcohol in 

 the method has many jn-actical disadvantages. He therefore made 

 some experiments in order to find a better solvent, and after a little 

 consideration came to the conclusion that paraffin of low boiling 

 point would probably dissolve the parafiin in which the sections are 

 imbedded more quickly than the guttapercha film to which they are 

 attached. This proved to be the case to a certain extent ; the gutta- 

 percha was, however, appreciably soluble. He therefore tried a 

 solution of raw caoutchouc in benzine, instead of guttapercha, with 

 perfectly satisfactory results. 



A thin solution of caoutchouc in benzine or chloroform is prepared 

 and poured over the slide so as to form a film in the same way that 

 collodion is poured on a photographic plate. When the film is dry 

 the sections are arranged on it, and the temperature of the slide 

 raised to the melting point of the paraffin ; the sections then fall on 

 to the indiarubber film which has become sufliciently sticky to adhere 

 to them perfectly. "When the slide is cold it is treated with naphtha 

 or any light paraffin oil, the solvent action being the more rapid 

 the lower the boiling point of the oil used. Absolute alcohol is 

 readily miscible vnth the naphtha or light paraffin, so that the 

 solvent is readily removed. The slide can now be placed in 

 successive alcohols, stained and returned to absolute alcohol. It is 

 now to be cleared with kreasote or oil of cloves and mounted in the 

 ordinary way. Apart from the great advantage of being able to 

 stain on the slide, this indiarubber method seems to possess some 

 points of superiority over the shellac method of Giesbrecht. This 

 depends on the fact that sections can be mounted in balsam direct 

 from the najihtha. The following are some of the advantages over 

 Giesbrecht's method : — 



1. The indiarubber is more uniform and therefore safer for small 

 objects. 



2. The indiarubber is dry and thus allows a more minute arrange- 

 ment of the sections on the slide. 



* Zool. Anzcig., vi. (1883) pp. 300-7. 

 t Bee this Journal, a7ile, p. 307. 



