ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
247 
counting the number that fall within the area of the block of 25 
squares. The red blood-corpuscles are most conveniently enumerated by 
counting the number which fall within the central square, which, to 
facilitate enumeration, is here divided into four smaller squares. The 
number of red and white blood-corpuscles in one cubic millimetre of 
blood can be conveniently arrived at by superposing the scale in turn 
Fig. 18. Fro. 19. 
upon ten different portions of the microscopic specimen, and by then 
multiplying the total red and white blood-corpuscles which were found 
in the areas which have just been specified by 10,000 and 400 respec- 
tively. 
In fig. 17, D represents the substage condenser, E the slide or haemo- 
cytometer-cell, and F the cover-glass. 
(5) Microscopical Optics and Manipulation. 
Knife and Strop for Microtomes.* — Herr G. Marpmann mentions 
the advances made in section-cutting since the introduction of the micro- 
tome ; he figures a knife made during the last 17-18 years by W. Walb 
of Heidelberg, and mentions a sharpening strop with rounded surface, 
also made by W. Walb. 
B. Technique.! 
(1) Collecting- Objects, including- Culture Processes. 
Nutritive Medium for Algae. — In his important work on Repro- 
duction in Algae and Fungi, J Dr. Klebs recommends, for the culture of 
Algae, the employment of both fluid and solid media. As a fluid medium 
he finds Knop’s the best, viz.: — 4 parts calcium nitrate, 1 part magne- 
sium sulphate, 1 part potassium nitrate, 1 part potassium phosphate. 
* Zeitschr. f. angew. Mikr., iii. (1897) p. 6 (1 fig.). ''***''' 
f This subdivision contains (1) Collecting Objects, including Culture Pro- 
cesses; (2) Preparing Objects; (3) Cutting, including Imbedding and Microtomes; 
(4) Staining and Injecting; (5) Mounting, including slides, preservative fluids, &c. ; 
(6) Miscellaneous. % Vide ante , p. 147. 
