242 
NOTES AND MEMORANDA. 
A New Slide for Exhibiting Infusoria is described by Dr. Hunt, 
who read a paper at a late meeting of the Biological and Microscopical 
Section of the American Academy of Natural Sciences. In this 
paper Dr. Hunt called attention to an ingenious slide invented by 
Mr. D. S. Holman for exhibiting infusoria, especially under the gas 
microscope. These slides are made by grinding a deep depression in 
a thick slide, and then making a very shallow circle all round the 
deeper central cavity. If the central depression be filled with 
the organization in water which is desired to be studied, and covered 
with a thin glass, in a short time the shallow circle all round the 
margin will be filled with minute bodies, often zoospores or other 
objects in the life history of the object in the deeper cell. The 
pressure of the atmosphere retains the cover in position. 
Photo-mechanical Printing. — Incidentally to a pathological report 
to the Surgeon-General, says the ‘American Naturalist,’ Sept. 1872, 
Dr. J. J. Woodward calls attention to the familiar disadvantages of 
the usual means of representing in publications the magnified appear- 
ance of microscopic objects by etchings, lithographs, and woodcuts. 
All such hand work is laborious and wasteful of time if done by the 
investigator, and liable to omit the most important points if entrusted 
to another artist. Even the microscopist himself, being unable to 
represent all that he sees, is obliged to select what he conceives to be 
of importance, and thus represents his own theories rather than severe 
facts. [If, however, his theories are correct, and his delineation skil- 
ful, this very power of selection and construction enables him to give 
a distinctness and completeness which is lacked by the photographic 
camera.] The advantage of truthfulness is on the side of photo- 
micrography, but silver prints are expensive, inconvenient, and not 
permanent, and the reproduction of the negatives in permanent inks 
is greatly desired. Two such methods are now successfully used in 
the United States. By the Woodbury method a relief surface of 
gelatine is produced from the negative by the action of light, and 
from this a metal “ intaglio” is produced by pressure. In this a 
series of suitably coloured gelatine films, which constitute the prints, 
are formed by mechanical means. Thus was produced the photo- 
graph of Amphipleura pellucida in the last April number of the 
‘ American Naturalist.’ In the Albertype process a printing surface 
(not a relief) is produced through the negative on a gelatine film by 
the action of light. The prints thus produced are, at present, less 
expensive than the Woodbury prints, and more convenient for book 
work, but the edition is less uniform. On enamelled paper the prints 
are handsomer, but will not bear much handling. 
The Angular Aperture of Immersion Glasses. — In the ‘ Ame- 
rican Naturalist’ for September, Dr. Josiah Curtis says that all 
lovers of progress in scientific research feel much pleased with the 
labours of investigators who make good use of the extensive means at 
their control, as well as also with the results which have emanated 
from the patient thought and close study of such men as Mr. Wenham 
and others abroad. “ We are very apt, however, to give too little 
credit to the intelligent instrument-maker himself. The mind which 
combines science with practice in its application has great advan- 
