ZOOLOGY AND BOTANY, MICKOSCOPYj ETC. 451 



spring, the other end of which is bent down vertically, and fastened 

 in the cleft of a split peg. This has a long oval handle projecting 

 upwards obliquely, and it is fixed in a hole in the object-holder of 

 the microtome, to a depth of from 2 to 3 cm. It can be turned in this 



Fig. 87. 



, hole, and fixed more or less deeply as desired, whereby the end of the 

 spring and the weight can be moved to a considerable extent laterally 

 or slightly perpendicularly. 



In practice, the position of the hole for the reception of the split 

 peg must be so arranged relatively to the length and curvature of the 

 spring, that the small weight rests lightly along its whole length on 

 the anterior part of the upper surface of the paraffin mass to be cut. 

 This can be easily managed by a slight lateral movement of the end 

 of the spring in the cleft of the peg. By turning the perpendicular 

 steel rod attached to the weight, the latter can be made parallel with 

 the edge of the knife. Slight alterations in the pressure of the weight 

 can be made by raising or lowering the rod in its tube ; greater alter- 

 ations, by a slight bending of the spring. 



On cutting the section the tendency of the anterior end to rise and 

 roll up will be restrained by the weight, and thereby the whole section 

 be prevented from rolling up. As the knife advances the weight 

 slides upon the blade, and the section always remains flat and even, 

 with one end held down by the weight and the other adhering to the 

 edge of the knife. 



It is easy to adjust such a section-stretcher to any sliding micro- 

 tome. 



Preparation of Marine Algae.* — Working under the inspiration 

 of Dr. Paul Mayer, G. Berthold has experimented with iodine and 

 other reagents on delicate marine algae. The aim was to find solutions 

 that would produce the least possible disturbance in the structure of 

 the cell-protoplasm. It was found that satisfactory results could not 



* Priugsheim's Jahrb. f. Wiss. Bot., xiii. (1882) pp. 704-5. Of. Amer. Natural., 

 xvii. (1883) pp. 456-7. 



2 G 2 



