ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 279 
the red blood-corpuscles which was first suggested in 1885 by Prof. 
Blix and later perfected by Dr. Hedin. 
In Dr. Hedin’s apparatus, represented in fig. 24, the glass tubes con- 
taining the blood are held securely by a spring in a brass frame at the 
top of an upright which is caused to revolve 104 times for one turn of 
the handle. In determining the volume of corpuscles the blood is 
mixed with an equal quantity of a fluid preventing coagulation and is 
then rotated, when the red corpuscles form a column at the periphery of 
the tube. 
Fig. 25. 
The author’s improved haematokrit (see figs. 25 and 26) presents 
the following advantages : — The tubes are double the length of 
those used in Dr. Hedin’s apparatus, viz. 70 mm., the lumen is reduced 
from 1 to 1/2 mm. in diameter, while the divisions on the scale out- 
side the tubes are increased to 200, so that the percentage is at once 
determined. A series of experiments made by the author on nineteen 
different solutions led to the choice of a 2J per cent, solution of 
bichromate of potassium as the most useful liquid with which to dilute 
the blood for counting red blood-corpuscles. When this diluting liquid 
was employed, 100 revolutions of the large wheel or 10,000 revolutions 
of the frame containing the tubes was found to be amply sufficient 
to secure a constant volume of red blood-corpuscles. Experiments 
made by the author upon twenty-five healthy men, with an average age 
of twenty- six years, in order to determine the normal volume and its 
