1883. Microscopy. 995 
say to 0.005™™ or in extreme cases to half that. It is not, how- 
ever, all tissues and objects that will admit of sections of such 
delicacy. Well-hardened liver may generally be cut to 0.015™™ 
this being about the diameter of the hardened cell, Occasionally, 
however, in this tissue, sections of 0.010™™ can be obtaine - 
phatic glands and brain may be cut to 0.010 or 0.075™™: em- 
bryonic tissues, well imbedded, usually admit sections of 0.005 
and 0.003™" In some cases even sections of 0.002™ thickness 
can be obtained. These numbers refer to the largest size of the 
microtome, and to serial sections. The two smaller sizes will 
give sections of the same delicacy, but comparatively smaller in 
extent of surface. The length of the sliding surfaces of the large 
instrument is 40°™ and the edge of the knife is 23% In the 
medium size these dimensions are 27 and 16 and in the small- 
est about 21 and 11“ 
Professor Thoma also adds some practical remarks on the use 
of the microtome and the necessary previous preparation of the 
specimens, it being his opinion that further progress in section- 
cutting is to be expected from the perfecting and development of 
the technical methods of preparing, hardening, soaking and im- 
bedding the tissues. Personally he feels sure that any tissue 
(excluding bone and teeth before decalcification) may be prepared 
so as to be cut to any degree of delicacy down to 0.002™ The 
microtome will work with sufficient exactness to permit this, but 
hitherto there are only a few tissues which we can prepare so per- 
fectly as to admit sections of such extreme minuteness. e 
following are the points to which he most especially wishes to 
draw attention: 
cut by freezing microtomes, for instance, on the simple and prac- 
tical instrument of Hughes and Lewis. The addition of a freez- 
ing apparatus to a thoroughly exact sliding microtome is neither 
advisable nor necessary. The differences of temperature pro- 
duced in different parts of the instrument would be apt to inter- 
fere with the perfect planeness of the sliding surfaces ; whilst, on 
the other hand, section-cutting with frozen tissues is so simple 
and easy with the ordinary freezing apparatus that any further 
complication in the way of a sliding support of the knife is 
Superfluous. 
tween the arms of the clamp attached to the carrier b (Fig. 1). 
he clamp should then be fixed in such a position that the speci- 
men is as near as possible to the knife-carrier. The knife will 
