178 
president’s address. 
Aug., 1889. 
crossed nicols when the quartz grain in which they are 
contained is in the position for extinction. A considerable 
number of flakes of a white mica lie among the quartz 
grains, but do not appear to belong to the original quartz, as 
they do not traverse the grains. Rounded grains of zircon, or 
at any rate of a mineral of very high refractive index, and of a 
white or pink, some even of darkish pink colour, occur pretty 
frequently in the quartz ; and a few fragments of tourmaline, 
showing the characteristic dichroism, are scattered through¬ 
out the section. Only very few grains of felspar are recog¬ 
nisable ; one shows multiple twinning. 
(To be continued.) 
BIRMINGHAM NATURAL HISTORY AND MICRO¬ 
SCOPICAL SOCIETY. 
PRESIDENT’S ADDRESS. 
BY W. B. GROVE, M.A. 
(Concluded from page 141.) 
The surfaces of all plants, the feathers of birds, the skins 
of animals, the human face, hair, hands, and garments, are 
all covered with Bacteria, or their spores, that have fallen 
upon them from the air. The ground itself receives, of course, 
the greatest number, and yet it is found by actual cultivation 
that the Bacteria of the soil are not entirely identical with 
those of the atmosphere. In the air, Miquel found by experi¬ 
ment that five kinds are always present, although he appeared 
to be incapable of deciding what those kinds are, with the 
exception of Cladothrix dichotoma. 
In the soil the Bacteria are confined to the superficial 
layers ; at a depth of 2ft. hardly any are found, and at 
a depth of 3ft. none. If particles of soil are crushed fine, 
and then sown on the surface of solid nutrient gelatine, as 
was done by Koch, we see the Bacteria which were in 
the soil develop in a number of little colonies. By this 
means Miquel has calculated that there exist in a grain of 
soil of the Park of Montsouris, on the average, 50,000 
bacterial germs, and in the streets of Paris between 100,000 
and 150,000. Adametz found in a grain of ordinary garden 
soil about 30,000. These are chiefly the putrefactive and 
fermentative Bacteria, but the pathogenic (disease-producing) 
species can also occur in the earth ; when sheep that have 
died of anthrax are buried, the soil is permeated with the 
spores, which are conveyed to the surface by earthworms, 
