642 SUMMABY OF CURRENT RESEARCHES RELATING TO 



The algje prepared in this way can readily be drawn or measured. 

 The cover-glass is carefully removed, and, if a low power or a dis- 

 secting Microscope is used, the object is taken up by a needle or stiff 

 bristle, and again at once placed in potassium acetate or glycerin. 

 If, on the contrary, the whole material thus prepared has to be got 

 ready for drawing or measuring, a drop of acetic acid is added after 

 removing the cover-glass. The algsB are in this way imbedded in 

 potassium acetate and glycerin, fluids perhaps the best adapted of 

 any for the preservation of algee. 



Dry mosses and fungi may also be prepared in the same way. 



Chapman's Microtome-* — A. B. Chapman has devised a micro- 

 tome, which has for its cutting surface two parallel glass-plates 

 cemented to a block of mahogany, through which is inserted a brass 

 cylinder at right-angles to the glass plates ; in this cylinder (which 

 forms the " well " of the microtome) an accurately fitted brass plug 

 works, carrying on its top a flat-headed table-like piece which entirely 

 prevents the imbedding agent from rising or turning round while the 

 sections are being cut. The plug is moved up and down by a brass 

 disk, which revolves between the block of mahogany and a similar 

 block underneath. The brass disk is graduated on the edge of its 

 upper surface, each graduation representing a movement of • 0005 in. 

 of the plug. The microtome has a base-board which can be firmly 

 clamped to a table, and the whole is so conveniently arranged that 

 every operation or adjustment can be made at once, the whole being 

 in view on the table. 



Use of the Freezing Microtome.t — The tendency at the present 

 time is to make all microscopic sections by the dry method after paraffin 

 infiltration and imbedding ; but no doubt there is a place, and an 

 important one, for the freezing microtome in practical histology, and 

 in this note S. H. Gage calls attention to what seem to him improve- 

 ments in its use. 



Disliking greatly the disagreeable mess made by ice and 

 salt, it occurred to him to take advantage of the device of plumbers 

 to thaw out water and gas pipes, — ^o use strong alcohol with 

 the ice or snow instead of salt. By using snow or finely powdered 

 ice and 95 per cent, alcohol, a temperature of 20 C. below zero is 

 obtained within five minutes, and this temperature may be maintained 

 with far less trouble than with ice and salt. The microtome used is 

 the Eutherford pattern, modified by placing the drain near the top 

 instead of in the bottom. A rubber tube passing from this drain to 

 a jar preserves the overflow. It requires about 250 c.cm. of 

 alcohol to freeze and keep frozen one tissue for cutting, but this is 

 not lost, as little evaporation takes place, and the dilution does no 

 harm for many purposes, hence the method is not wasteful, while it is 

 much more pleasant and expeditious than with salt. 



Ordinarily tissues are infiltrated with thick gum before freezing, 



* Sci.-Gossip, 1884, p. 137. 



t Science Kecord, ii. (1884) pp. 134-5. 



