ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
571 
the microscopical examination of potable water. The author’s aim is to 
make the biological method a check on the chemical analysis, for it is 
only by an accurate investigation of the number and character of living 
organisms that the exact value of free and albuminoid ammonia can be 
estimated. The present monograph only deals with non-bacterial 
organisms, and is divided into two parts, the first of which treats of 
methods, apparatus, &c., required for making a qualitative examination 
of a water supply. In the second part the subject is treated quantita- 
tively, the author showing how the organisms may be counted, and 
the inferences to be derived from their specific characters though “ the 
sanitary significance and relative economic importance of the micro- 
scopical forms will be treated in another volume.” 
Filtration of Water through Stone Filters* — Prof. E. von Esmarch 
finds that the ordinary stone filters are, like charcoal filters, quite useless 
for sanitary purposes since they are only capable of removing the coarser 
impurities from turbid water. In one respect, indeed, they make matters 
worse, since they actually aid in propagating the poison they are pre- 
sumed to remove from the tainted water. The filters experimented with 
came from various parts, their filtering bed being composed of lava, tufa, 
or of sandstone. Naturally the great point to be ascertained was whether 
these filters would remove bacteria, and this was done by passing through 
Berlin water to which some pigment-forming bacteria had been pre- 
viously added. It was found that the germs not only passed through, 
but after a certain lapse of time actually increased. It was obvious, 
therefore, that this increase must take place in the pores of the filter, a 
result which does not seem at all surprising since filters are not prone 
to possess a germicidal action, and it must be pointed out that the 
conditions of the experiment were unusually favourable for the develop- 
ment of microbes and quite different from those under which water 
is usually filtered. For example, a considerable quantity of organic 
matter, i. e. of the cultivation medium, must have been mixed with the 
water. All the same the experiments are worthy of record, as the use 
of filters no doubt leads to undue confidence in their virtue. 
The Microscopic Structure of some Australian Bocks.f — The Rev. 
J. Milne Curran, in the concluding part of his paper, says : — “ A micro- 
scopic examination of our rocks points to the existence in Eastern 
Australia of every leading type from the vitreous to the holo-crystalline 
condition, both acidic and basic, and their general microscopic structure 
conforms to well-knowm types of described American and European 
rocks. In writing of American basalts, Zirkel says,! * It is worth 
while to pause, and remark that in these widely remote quarters of the 
globe, the product of the solidification of a molten mass, although 
exposed to many casualties, has, nevertheless, maintained a surprisingly 
close identity of microscopical composition.’ The remark applies in 
every particular to the Australian basalts described in this paper. 
Within well-defined limits, the structure of our basalts shows micro- 
* Centralbl. f. Bakteriol. u. Parasitenk., xi. (1892) pp. 525-31. 
t Journ. and Proc. Roy. Soc. N.S. Wales, xxv. (1891) pp. 179-233, pis. xx.-xxii. 
+ U.S. Greol. Explor. Fortieth Parallel, vol. vi. Microscopical Petrography, 
p. 253. 
