188 General Notes. [ March, 
mass by reason of diminished pressure, shrinkage in the mass having con- 
tinued to occur after the external portion had become hardened into an 
immovable crust; a theory which is confirmed by the effects on polar- 
ized light, the central portions of the mass having no power to depolar- 
ize the light, while the marginal portions depolarize it in such manner 
as to indicate a strain caused by pressure in the line of the circumference 
and not in the line of the radius. Similarly, the black crosses seen un- 
der polarized light in certain portions of the amber, having as nuclei 
either air bubbles or minute solid angular bodies of a sand-like appear- 
ance, are of a character to indicate not increased but diminished pressure 
from within, not an expansion of the contents, or a contraction of the 
surrounding material upon it as is the case with minute crystals inclosed 
in diamonds, but a shrinkage of the contents of relatively hardened lay- 
ers surrounding the bubbles or granules. 
Farse Licur Exciuper. — E. Gundlach of Rochester, N. Y., 
mounts his new two-inch lenses with a brass tube $ inch long projecting 
below the front surface of the objective and having a perforated dia- 
phragm at its lower end. This cuts off much of the stray light that 
would otherwise enter, and still leaves 14 inch of working focus. 
New Ossects. — The very interesting preparations of recent and 
fossil diatoms, by Dr. R. S. Warren, of Waltham, Mass., can now be ob- 
tained from Mr. Charles Stodder, of Boston. Many of the slides, espe- 
cially those from Savannah and the Isles of Shoals, contain new or rare 
forms. 
Charles Zentmayer, of Philadelphia, son of the well-known Joseph 
Zentmayer of the same city, is preparing double-stained vegetable tis- 
sues with great success. The coloring is excellently distributed and the 
cell peculiarity well preserved. 
DENTITY OF THE Rep BLoop Corpuscies IN Dirrerent Hou- 
MAN Races. — Dr. J. G. Richardson, of Philadelphia, well known as 4 
leading advocate of the possibility of distinguishing by measurement the 
blood corpuscles of man from those of many of the familiar domestic 
animals, has recently extended his researches to the blood corpuscles of 
the different races of mankind, with a view to determine by comparative 
study whether they are identical or not. Taking advantage of the P 
portunity afforded by the International Exhibition at Philadelphia, he 
obtained, in some cases with considerable difficulty, permission to secure 
specimens of their blood from a considerable number of the members 
and attachés of the foreign commissions present at the Centennial. A 
finger having been suddenly pricked with a cataract needle, the "e 
the exuding drop of blood was touched to the centre of a glass slide, an 
the small drop thus obtained was spread by means of the edge of another 
slide, after Dr. Christopher Johnson’s excellent method. In the dried 
film the corpuscles were measured by a cobweb micrometer whose aas 
ing, as actually employed in this work with a y immersion objective 0 
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