REPORT OF THE MICROSCOPIST. 
Sir: I have the honor to submit herewith my sixteenth annual 
report. 
Since the publication of my first official bulletin, in 1884, relating 
to the microscopical methods of detecting butter substitutes, there 
has been a continued demand for information on this subject from 
all parts of the United States, extending to Great Britain, France, 
Germany, etc. 
The inquiry for more and fuller information respecting this branch 
of my division comes from a large number of those more or less in- 
terested, professionally, in the classification of animal and vegetable 
fats as determined by microscopical observations. F'armers, dairy- 
men, inspectors of butter and milk, presidents of boards of health, 
physicians, chemists, microscopists, and the general public have 
expressed a deep interest in this subject. 
n my first experiments, a notice of which was published in the 
New York Quarterly Microscopical Journal, 1879, vol. 2, with illustra- 
tions, and also in the Scientific American for the same year, I found 
that the detection of oleomargarine was comparatively easily accom- 
lished with the lower powers of the microscope and plain trans- 
mitted light. The material, as then sold, was highly crystalline, 
and animal tissues, even to minute blood vessels, were found in it. 
About this time the managers of an oleomargarine factory in Balti- 
more, Md., supplied me with samples of their oleemargarine, by an 
examination of which I was able to convince them that their prod- 
uct contained animal tissues and other impurities. They soon de- 
vised means to remove these impurities in the process of manufact- 
ure. But the object of my labor being rather to detect oleomargar- 
ine than to purify it, it became necessary to improve my methods 
for this purpose, as, by the employment of skilled chemists, the com- 
position became more and more difficult of detection by means of 
lain transmitted light only. JI therefore resorted to polarized 
Fight, which enabled me to distinguish the forms of the respective 
fats found in oleomargarine compounds. 
With regard to the differentiation of crystals of butter and fats, 
as shown under the microscope, great progress has been made during 
the past year, not only in the methods of determining one fat from 
another, but also in the production of very cy es micro-photo- 
graphs of them, and still further in the reproduction of these, by 
newly improved photo-mechanical processes. But no process of re- 
roduction will ever wholly represent the minute structure of the 
fatty crystals as viewed by the microscope, for reasons obvious to ex- 
perts. 
617 
