634 SUMMARY OF CURRENT RESEARCHES RELATING TO 



plate. Several diaphragm-plates should be prepared in which the 

 slit varies in extent from a half to a whole of a quadrant or more. 



The following mixture, which is Meckel's fluid with the addition 

 of a little acetic acid, is recommended above all other reagents as a 

 preservative medium : 



Chromic acid 1 part. 



Platinum chloride 1 „ 



Acetic acid 1 „ 



Water 400-1000 parts. 



Unicellular animals die very slowly in this mixture, and suffer 

 very much less alteration in structure than when killed in osmic acid 

 or picro-sulphuric acid. 



A special method is required for Protozoa filled with opaque food- 

 material. In many cases the nucleus and the structure of the cell- 

 body are completely obscured by foreign bodies. The method 

 adopted in such cases is as follows :— 



(1) Placed in picro-sulphuric acid 3-4 minutes. 



(2) Transferi'ed to boiling hot water for a short time. 



(3) Placed in water and a little ammonia added ; this causes the 

 contracted object to swell up to its original size and form. 



(4) Neutralize the ammonia with a little acetic acid, and then 



(5) Colour with borax-carmine or ammonia-carniine. 



(6) Wash and examine in dilute glycerin. 



The picro-sulphuric acid destroys the nutritive material; the 

 ammonia dissolves any particles of fat that may be present ; and thus 

 the object becomes transparent as far as possible. 



A concentrated solution of corrosive sublimate may also be used 

 with success for killing Protozoa ; but care must be taken to wash 

 thoroughly. 



Dr. Brass has obtained his best results without reagents or dyes. 



Bom's Method of Reconstructing Objects from Microscopic 

 Sections.* — Dr. G. Born describes in detail a very ingenious method 

 of constructing models of objects from serial sections. By the aid of 

 the camera the outlines of the sections are transferred to wax plates, 

 which are then cut out so as to correspond in outlines as well as 

 dimensions to the sections equally magnified in all three directions. 

 With plates thus prepared, it is only necessary to put them together 

 in the proper order to obtain a complete model. The method is 

 simple and extremely useful, especially in investigating objects with 

 complex internal cavities. Born has made use of the method in 

 studying different parts of the vertebrate head ; Swirski, in eluci- 

 dating the development of the shoulder-girdle of the pike ; Stohr, in 

 tracing the development of the skull of Amphibia and Teleostei ; and 

 Uskow, in studying the development of the body -cavity, the 

 diaphragm, &c. 



* Arch. f. Mikr. Anat., xxii. (1883) pp. 584-99. Cf. Science, ii. (ISSSJ^^p. 802, 

 and Amer. Natural., xviii. (1884) pp. 446-8. ' 



