INVEETEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 



1037 



Time of freezing is about seven minutes, except in very warm weather, 

 when it requires a few moments longer. The instrument does not 

 work so satisfactorily in warm weather, owing to the rapid melting of 

 the surface of the preparation. It is absolutely necessary that the 

 mass should be frozen solid, or the sections cannot be cut smoothly. 

 An extra freezer may be employed, and 

 while one specimen is being cut the other Fig. 111. 



may be frozen, and by exchanging cylinders f 



(they being interchangeable) no delay is /f^^^^^^^^ 



necessary to its continuous operation. // _..._.7\\ 



The art of cutting is readily acquired, ''" e 'H 



and when the preparation is frozen it is the V:;^ ----^— — '.'/ 



work of a few moments to obtain several o/'"\ ' V^}'// /""n 

 hundred sections. Two hundred sections or ^-r^-1il■^.f^ '^r-^-j-''l 

 more, if desired, can be made each minute V-' ~ i |ji|H R >;,V 

 and of a uniform thickness of about ^L of ; i:^^[~|jl!]i| ^^^ i 

 an inch (thinner or thicker, from about | ,l^-rj--in|l[---^l j 

 5^ViT inch to about t^^^ inch, according as ciy-"-"' ^'^^ ^.^ / 



the pointer is set). The delivery, ease, and ~"--— /> ' 



rapidity with which they can be cut, must ^ 



be seen in order to be appreciated. It is a, B, tube containing spe- 



not necessary to remove the sections from cimen, which is surrounded 



the knife every time, but twenty or thirty ^y freezing mixture in tiio 



may be permitted to collect upon the blade ; fceiver C, D E,F, revolving 



*i T 1 J r ^1 3 i.1 ^ -r I'opper, With wings W, W, 



they he curled or folded up upon the knife, f^r stirring the ice G, outlet 



and when placed in water straighten them- for melted ice. 



selves out perfectly in the course of a few 



hours. The knife is an ordinary long knife from an amputating 



case. 



Perfectly fresh tissues may be cut without any previous prepar- 

 ation, using ordinary mucilage (acaci39) to freeze in, but most speci- 

 mens require special preparation. If preserved in Miiller's fluid, 

 alcohol, &c., they require to be washed several hours in running 

 water ; then according to the suggestion of Dr. D. J. Hamilton,* the 

 specimen is placed in a strong syrup (sugar, two ounces ; water, one 

 ounce), for twenty-four hours, and is removed to ordinary mucilago 

 aeaciaa for forty-eight hours, and is then cut in the freezing micro- 

 tome. 



The sections may be kept indefinitely in a preservative fluid : 

 R glycerin®, 5iv ; aqua) destil. 5iv ; acidi carbolici, gtt. iij ; boil and 

 filter. The addition of alcohol 5U is advisable. 



Salicylic Acid as a Preservative. f — Mr. A. Micklc has had very 

 good success witli salicylK; acid in mounting vegetable preparations 

 of all kinds. One diHiculty, however, is that it dissolves very 

 8j)aringly in water, and alcohol j)roduces clianges wliich are frequently 

 undesirable. It is well known tluit salicylic acid dissolves freely in 

 a solution of borax, and it is also familiar to most persons that borax 



* Soo " A Now Method of Prppftiing liHrgo Sections of Norvoiis Centres for 

 Microscopicni Fnvostigalion."— • Journ. Anat. and I'liys.,' vol. xii. 

 t 'Am. .lourn. Micr.,' v. (1880) p. 185 (>. 



VOL. HI. 3 z 



