ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
835 
“ adding and counting register,” which is fixed to the tightening-bar of 
the Microscope. 
After giving illustrative cases, the author makes some remarks on 
the multiplication of tubercle bacilli in sputum outside the body, and 
then gives a short demonstration of the accuracy of the method. 
Colloidal Clay for Filtering Fluids containing Bacteria.* — Dr. H. 
Aronson uses argillaceous earth, from which he prepares the hydroxide 
of aluminium for filtering purposes in the bacteriological laboratory. 
The aluminium hydroxide is precipitated as a gelatin-like snowy mass 
from a 12 per cent, solution of sulphate of alumina or alum by means 
of excess of ammonia. After settling, the supernatant fluid is partly 
decanted and partly siphoned off, and the residue washed with dis- 
tilled water until its reaction is completely neutral. The colloidal 
mass is then spread on the plate of Hirsch’s porcelain filter and distri- 
buted so as to form an even layer, and the whole then sterilized in an 
incubator at 140° ; previously to this any excess of fluid may be removed 
by a suction-pump in the usual way. 
In this way is obtained a filter-mass which is at once uniform and 
homogeneous. Occasionally, after removal from the incubator, cracks 
and fissures may develope in the mass ; these may be avoided by adding 
a little boiling sterile water before the mass have had time to cool. 
The filtrates obtained by means of this medium seem to have been 
successful in most cases. The apparatus, however, will tolerate only 
very low suction-pressures, as anything like a high pressure produces 
cracks and clefts in the filter-mass. 
Some Suggestions in Microscopy. f — Mr. G. M. Hopkins, writing in 
the ‘ Scientific American,’ says: — “ An object which always interests the 
microscopist, and excites the wonder and admiration of those who regard 
things microscopic from the point of popular interest, is the circulating 
Fig. 91. 
blood in living creatures. Nothing in this line has proved more satis- 
factory than tho microscopic view of the circulation of blood in the tail 
of a goldfish. Thanks to Mr. Kent’s invention of the fish-trough, the 
arrangement of the fish for this purpose has been rendered comparatively 
simple and easy. 
* Archiv f. Kinderheilkunde, xiv. (1891) pp. 54-8. 
t English Mechanic, liii. (1891) p. 494. 
