ZOOLOGY AND BOTANY, MICROSCOPY, ETC, 1065 



these pour the liquid to be crystallized, and having warmed the other by 

 passing it through the flame of the lamp or dipping it in hot water, place 

 it immediately on the top of the globule of fluid, letting it settle to place 

 of its own weight. The fluid is thus spread out into a tenuous film between 

 the two watch-glasses. Now place the watch-glasses upon a piece of felt, 

 two or three thicknesses of blotting-paper, or some other non-conducting 

 material, and with a pipette pour on to the cavity of the upper glass a half 

 fluid drachm of rhigoline, benzol, or ether, and blow on it with the lips. 

 As the temperature falls the film of liquid begins to deposit crystals ; 

 sometimes this occurs instantaneously, usually it requires about fifteen 

 seconds to a minute to thoroughly cool the glasses. If necessary, the 

 process must be repeated. 



As soon as the deposition of crystals ceases take a bit of blotting-paper 

 and pass the edge of it between the glasses to absorb the remaining mother 

 liquor, leaving the crystals nearly dry. The upper glass is then removed 

 and the crystals in the lower glass may be examined at once under the 

 Microscope or collected and washed. 



It is presumed that the liquid to be crystallized is in a concentrated 

 state : if not, the small quantity required for this process is easily thickened 

 by placing the glass on a hot slide for a few moments. Where the opera- 

 tion must be repeated, it is best to use a clean glass for each portion, or to 

 carefully remove the crystals resulting from previous refrigerations, since 

 the second crop has a tendency to form around and on the first, thus making 

 masses too large for convenient examination with high powers. The use of 

 the pipette for placing the volatile fluid in the upper watch-glass is recom- 

 mended, because of the difficulty of pouring small quantities of readily 

 flowing fluids with any exactness, and the consequent danger of overflowing 

 and mixing with the fluid to be crystallized. 



Method of obtaining Methaemoglobin Crystals.* — Prof. W. D. Halli- 

 burton recommends the following easy method for obtaining methsemo- 

 globin crystals. A few cubic centimetres of the defibrinated blood of a 

 rat, guinea-pig, or squirrel, have added to them an equal number of droj)s 

 of nitrite of amyl, and the whole is shaken vigorously in a test-tube for a 

 minute or so. As soon as the liquid becomes chocolate-coloured a drop is 

 placed on a slide and covered. In a few minutes crystals of methaemoglobin 

 are formed, and if the edges of the cover-glass be sealed they may be kept 

 unchanged for several months. From guinea-pigs' blood the crystals thus 

 obtained are tetrahedra ; from squirrels' blood they are perfectly regular 

 hexagonal plates, as are also those from rats' blood ; but in the case of the 

 last there were a few other plates which, in the opinion of Mr. L. Fletcher, 

 are merely variations of the hexagons. 



Fearnley's 'Elementary Practical Histology.'! — This book has a 

 feature which is extremely novel in a histological work, viz. it contains an 

 account of the Diffraction Theory (under the head of " Immersion Lenses "), 

 with diagrams illustrating Prof. Abbe's leading experiments. The author 

 has been recommended | to omit this portion in future editions, a recom- 

 mendation which we hope he will not adopt. His reviewer, like so many 

 histologists, has evidently not appreciated the practical importance of the 

 discussion ; but one good effect of the book will, we have no doubt, be to 

 make many practical workers with the Microscope acquainted with one of 



* Quart. Journ. Micr. Sci., xxviii. (1887) pp. 201-4. 



t Fearuley, "W,, ' A Course of Elementary Practical Histology,' xi. and 363 pp., 

 46 figs. (8vo, London, 1887). J Nature, xxxvi. (1887) pp. 481-2. 



