86 _ THE AMERICAN MONTHLY [Apr 
inch constitutes a diameter in microscopy. The word 
misleads and confuses him. A magnification of ten dia- 
meters is a picture whose diameter is ten times as great 
as that of the object magnified. Ratio only is expressed. 
So we cannot tell him the part of an inch unless we know 
the diameter of the object magnified. Buy Gage’s book 
and it will explain a hundred such difficulties. 
L. A. Witson of Cleveland,. Ohio, died Dec. 15, 1901. 
He had been a close student of the microscope for many 
years and a contributor of both money and articles to the 
Journal. He had a large collection of lichens and liver- 
mosses, classified and catalogued, which his widow would 
like to dispose of. If possible to doso she will sell them. 
If not, we suppose they may be donated to some public 
institution. 
MICROSCOPICAL MANIPULATION. 
PRESERVATION OF URINE.—According to Dr. Schweiss- 
inger, in the Pharmaceutische Centralhalle, thymol is the 
best agent for the preservation of urine for examination 
with the microscope. It prevents fermentation of all des- 
criptions, and does not interfere in the re-action of the 
constituents. A granulet, the size of a pin’s-head, will 
suffice to preserve a hundred cubic centimeters of urine 
for a long time. 
DiIsEASE OF TURNIPS.—Turnips are subject to a para- 
site called Pseudomonas campestris which has been ex- 
amined by HE. F. Smith. He made a culture of this bac- 
terium and innoculated the turnip leaves through needle 
pricks. After 52 days, the leaves were shrivelled. Sec- 
tions of the root showed abundance of bacteria. No fung- 
us or animal parasite was found, but cultures from the in- 
terior of the root yielded P. campestris. He fixed the 
root with strong alcohol, infiltrated with paraffin, cut 
with sharp knife, mounted with water, plus $ per cent gel- 
