248 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
with the development of the lower animals and plants, the variation in 
the number of plankton organisms, &c., biologists should use sectional 
paper ruled logarithmically, or should use the ordinary sectional paper 
as if the distances at which the lines are drawn represented the logarithms 
of numbers, and not the numbers themselves. For most purposes it is 
sufficient if the paper be ruled or taken logarithmically in one direction 
only, the ruling in the other direction proceeding arithmetically as usual. 
Logarithmic plotting has two great advantages over the ordinary 
method, viz. : — (1) it allows of the graphic representation of an enor- 
mous range in the numbers dealt with ; and (2) it shows the same pro- 
portionate changes by lines having the same angle of slope, which 
implies that similarly shaped curves denote the same relative course of 
events. Some data relating to six species of diatoms, a rotifer, and 
two species of Entomostraca, taken from Apstein’s ‘Das Susswasser- 
plankton’ are plotted on the plate accompanying the paper in illus- 
tration of the method. 
Aitken’s Dust-Counter.* — Dr. A. Macfadyen and Mr. J. Lunt de- 
scribe the apparatus devised by Dr. Aitken for counting particles of 
dust in samples of air. The dust particles are rendered visible by 
supersaturating the air with vapour, whereby each particle becomes a 
centre of condensation. The essential parts of the apparatus are a metal 
box, in the top of which is a pair of biconvex lenses, and in the bottom 
a micrometer-plate etched into squares. The box is lined with bibulous 
paper moistened with water. The bottom of the box has a couple of 
perforations, one on each side of the micrometer-scale. Into one is 
fitted an air-pump, and into the other a tube supplied with three taps, 
which regulate the quantity and quality of the air allowed to pass into 
the box. The cooling of the vapour is effected by the air-pump, which 
rarefies the air. If no dust be present no dew-drops fall, while, when 
dust-laden air is allowed to enter, a fine rain of dew-drops is deposited 
on the micrometer. Though extremely ingenious and of great scientific 
value, the instrument does not appear to be of much practical use, at 
present at least, for hygienic purposes. 
Enumeration of Blood-Platelets, f — Drs. T. G. Brodie and A. E. 
Russell have made an elaborate series of experiments to ascertain the 
best way to enumerate correctly the number of platelets in a given 
quantity of blood. The chief difficulties in this examination are due to 
the fact that the platelets have a great tendency to stick together, and 
that the red corpuscles become invisible from the action of reagents. 
The method adopted by the authors was to obtain blood from the finger, 
either puncturing through a layer of the diluting fluid, or dropping the 
blood into a glass vessel containing the fluid. The fluids selected after 
numerous trials were solutions of dahlia in strong glycerin or diluted 
glycerin ; but excellent results were obtained from equal parts of glycerin 
saturated with dahlia and 2 per cent. NaCl. These solutions have the 
disadvantage of dissolving out the haemoglobin from the red-cells, so that 
the stroma eventually becomes invisible ; but as this action takes some 
time, it is easily possible to complete the enumeration. By adding 
* Trans. Brit. Inst. Preventive Med., 1st series, 1897, pp. 142-51 (1 pi.). 
f Journ. Physiology, xxi. (1897) pp. 390-5. 
