ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



489 



metal. The end of the arm is expanded in order to be more readily- 

 heated. The sides of the hot chamber or box are of unequal thickness, 

 the side farthest from the arm being the thicker, in order that the 

 temperature of the side from which the arm projects and that of the 

 opposite side may be about equal. This is shown by putting little 

 pieces of paraffin on the top of the box, for they melt at almost the 

 same time. A thermometer is placed within the chamber to mark the 

 temperature, and this may be made to rise more or less quickly, ac- 

 cording as the expanded end of the arm is more or less heated, and 

 thus the temperature be kept fairly equable. If, however, a constant 

 temperature be necessary, the author advises the use of M. Vignal's hot 

 stage. The one described, however, is much more simple, and quite 

 suitable for most purposes. The instrument may also be used for cooling 

 down preparations by using methyl chloride on the expansion at the end 

 of the arm. 



Hallsten's " Compressorium."* — Dr. K. Hallsten apologetically calls 

 his apparatus a compressorium for want of a better name, for its main 

 use is intended to safeguard the face of the objective from the deposit of 

 vapour while examining the circulation of 

 the blood, e. g. in the chick. It may, 

 however, be used as a compressorium for 

 flattening out or exerting equal pressure 

 upon the parts of a specimen. 



The apparatus (fig. 79) consists of a 

 cylindrical brass tube H, which surrounds 

 the objective and carries the cover-glass D 

 so that watery vapour is prevented from 

 reaching the objective or face of the lens. 

 R is a ring into which the upper end of the 

 brass tube is screwed. This ring is screwed 

 in between the body-tube T and the objec- 

 tive 0. The cover-glass DD is fixed to the 

 lower end of the compressorium tube by an 

 alcoholic shellac solution. When in use the 

 tube can be screwed down so that the cover- 

 glass penetrates within the examining fluid 

 and comes in contact with the blastoderm, and observation is unhindered 

 by the presence of vapour. 



When the apparatus acts as a compressorium, the action is effected 

 by merely screwing or pushing the tube down upon the object. 



Hardy's Growing Slide. — Mr. J. D. Hardy writes : — " The absolutely 

 necessary qualities of a growing slide are that there should be a perfectly 

 free current, that the water supply should be pure or devoid of any 

 extraneous matter, and that the object should be observable at any time. 

 To carry out these desiderata I use apparatus shown in fig. 80 consisting 

 of the old 'animalcule box' of 1£ in. in diameter. At the upper part of 

 the raised cylinder a small vertical slit is made half-way down. On the 

 opposite side a hole is drilled in the bottom of the groove which runs 

 round the central glass disc. A hole is drilled in the side of the cap 

 about half-way down, so that when the cap is pressed close down the 



* Zeitschr. f. Biol., xxii. (1886) pp. 404-7 (1 fig.). 



