ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 707 



Talc for Cover-glasses with High Powers. — Mr. W. S. Kent 

 found * that in using the high-power objectives necessary for the 

 examination of the minute collar-bearing Flagellate Infusoria, the 

 chief obstacle was presented by the necessity for very thin cover-glass, 

 which causes both inconvenience and loss of time on account of its ex- 

 treme brittleness. Where the objects under examination are attached 

 to more solid substances, such as the stems of water-plants, this rigidity 

 and brittleness of the cover-glass hampers progress in a most pro- 

 voking manner, and materially restricts the limits of clear vision. 



The unsuitability of ordinary cover-glass for such investigations 

 led the author to provide a substance that has been productive of the 

 most satisfactory results. This was the ordinary talc, formerly 

 universally employed by microscopists, and now extensively used for 

 gaselier shades. This, with a little practice, may be split into laminae 

 of such extreme tenuity that they may be blown away with the 

 lightest breath, while for perfect evenness and transparency they will 

 compare favourably with the finest manufactured glass. With the em- 

 ployment of these talc-films the investigation cf Infusoria with the -^, 

 -^-^, or even the jJ^-inch objectives becomes, Mr. Kent says, a compara- 

 tively easy task. The material possesses the further considerable 

 advantages of bending readily and permitting the objective to be 

 brought close down on the more remote objects in the field, while it 

 may be cut with the scissors to any required size or shape. 



Micrometrical Researches on Contracted Muscle. j — Professor 

 T. W. Engelmann publishes an interesting series of measurements. 

 illustrating the relative lengths of the principal constituents of 

 muscular fibres during contraction. His observations were made 

 chiefly on beetles. They confirm and much extend, from a physio- 

 logical point of view, the histological results of Foettinger. i Against 

 Eanvier, Engelmann maintains the superiority of insects to vertebrates 

 for these studies. Every student of the more minute phenomena of 

 muscular action will read through the whole of this short paper, with 

 its tables too numerous for quotation. 



Prismatic Action of certain Microscopic Objects. § — The colour- 

 changes presented in the Microscope by various substances (chiefly 

 mineral) of uneven sui-face, when immersed successively in liquids of 

 different refracting power, have been made by Herr Maschke the 

 basis of a method of distinguishing substances. Such changes may 

 be had, e. g. with small glass particles, observed in water, in oil of 

 almonds, and in mixtures of the latter with oil of cassia. The dark 

 and the bright parts of the image show difterent series of colours. 

 That the efiects are simply due to prismatic action of the object 

 appears from the fact that they may be got without the Microscope, 

 by looking through a tube at a piece of rock-crystal in water, &c. 



For mineral objects Herr Maschke used five liquids — amylic 



* Kent's 'Manual of the Infusoria,' i. (ISSO) pp. 115-16. 



t Pfliiger's Archiv, xxiii. (ISSO) pp. 571-90. 



J See this Journal, iii. (1S80) p. 612. 



§ Wied. Ann., No. 12. See ' Nature,' xxih. (ISSl) p. 398. 



