ZOOLOGY AND BOTANY, MICROSCOPY, ETC. Ill 
germs on nutritive media. Tlio bacteria to bo cultivated are first 
disseminated in a small quantity of sterilized water, and some of this is 
then run over the plate, made of gelatin, serum, vegetable albumen, and 
the like. The capsule and plate are then placed under the bell of a 
powerful air-pump. If this work well the water is soon evaporated, 
leaving the germs behind scattered all over a smooth surface. Care 
must be taken not to make the surface too dry. This procedure is said 
to offer the advantage of allowing the inspection of the characteristic 
shape of superficial colonies at very early stages. Inoculations are 
easily made from any particular colony, and counting the colonies is 
much facilitated. 
Culture of Diatoms.* — Dr. P. Miquel states that a very favourable 
medium for the artificial culture of freshwater diatoms is ordinary fresh 
water in which have been thrown stems of grasses, the cortical substance 
of grains of wheat, barley, or oats, fragments of Muscineae, &c. ; soluble 
carbohydrates, albuminoids, &c., have an injurious rather than a favour- 
able influence. The presence of a very small proportion — from 1 to 5 
per mil. — of certain salts, such as those of soda, potash, or lime, in the 
condition of chlorides, bromides, iodides, phosphates, and sulphates, has 
a marked favourable effect on the multiplication of diatoms ; but they 
appear to prefer to obtain their silica from that set at liberty by the 
decomposition of plants rather than from soluble silicates. The marine 
kinds are easily cultivated in artificial sea-water, especially if containing 
fragments of Fucus or other sea-weeds. 
In another paper on the same subject, the same author j gives full 
instructions as to the best mode of cultivating diatoms, both freshwater 
and marine, the best media for their growth, the most favourable tem- 
perature, light, &c. The most destructive enemies to diatoms are 
bacteria. An apparatus is described for their culture free of bacteria. 
Cultivation of Diatoms.J — Dr. L. Macchiati, in a preliminary com- 
munication, points out that diatoms are easily cultivable in the nutritive 
solutions used in vegetable physiology, provided that a few drops of 
silicate of potash be added to the medium. Or the very water which 
the diatoms inhabit may be used. This, when filtered, and with the 
addition of a few drops of strong silicate of potash solution, forms an 
excellent fluid. The medium, placed in a watch-glass, is then inoculated 
with a loopful of the water inhabited by the diatoms, and the two fluids 
having been thoroughly mixed together by stirring, a loopful of the 
mixture is placed on the surface of a cover-glass, the exact thickness of 
which is previously ascertained. To the margin of the cavity of a 
hollow-ground slide is then applied some vaselin, and this is carefully 
placed over the cover-glass. The slide, now containing a hanging drop 
cultivation, is turned over. 
In such a drop the diatoms are in an almost natural state, and their 
development and mode of life may be watched under a power as high as 
1/18, though the lens commonly employed by the author is a dry apochro- 
matic with focal distance of 4 mm. and N.A. 0*95. In combination 
* Comptes Rendus, cxiv. (1892) pp. 780-2. 
t Le Diatomiste, 1892, pp. 73-5, 94-9, 121-8, 149-56 (3 figs,), 
f Jourm. de Micrographie, xvi. (1892) pp. 1 1 6—20. 
