THE MICROSCOPE. {2T 
With the same apparatus it would require too long.a tube, with 
in.; and still more forcing to raise the scale to read microns(the micro- 
metical unit. of 0.001 mm. or about 5;4,, in.) on the broad spaces, 
and 00.1 # (ss7yy7 in.) on the small. This standard, however, is 
available to those who possess such comparatively rare luxuries as 
a 5i,th in. objective (or over) and apparatus to match, with the skill, 
yet more rare, to use them to advantage. In such case the sheep’s 
blood dise will extend from line “4” to the Sth of “a”, or 44 and 8 
tenths (— 4.8 “). The human dise will now extend from line “2” 
to the 4th in “b’; but from ‘“‘b” to “2” counts 7, giving a reading 
of 7.4 “4, the upper figures representing the tens from “b” as the 
lower figures did from “a”. Still larger objects would carry the 
count back toward ‘10’, or beyond; though it would be better to 
return to a lower power than to attempt fine measurements near the 
edge of the field. But experts will be likely to use a different micro- 
meter, as follows, with such high powers. 
The “ filar,”’ or ““cobweb” micrometer, a more clumsy, elaborate 
and costly apparatus, requiring an expert manipulator with a heavy 
‘stand, is free from the limitations of the ruled plate and is far pre- 
ferable for very fine work. Its scale can be arranged to read mil- 
lionths of an inch as readily as thousandths, while its two movable 
lines of cobweb or platinum wire leave the field practically unob- 
structed, and, as seen moving across the flatter field of the positive 
achromatic ocular, can be brought up to the edges of the image to be 
measured with great definiteness and precision. The practical effi- 
ciency of this method, in exceptionally experienced hands, and from 
the average of many trials upon very favorable objects, has long been 
known to reach the limit of 5,455 in-; and the writer has often 
reached the same limit in micro-legal investigations. There seems 
to be no reason why this record should not be surpassed. 
PACPHO.LO'G Y. * 
Draenosis or Karty Paruisis By rae Microscope. t—Troup empha- 
sizes the diagnotic value of elastic fibres in cases of suspected 
phthisis, and says that “ in no case will they be missed if sought for 
with sufficient patience. They are to be found very early in the dis- 
ease and in the most innocent-looking sputum. They will be dis- 
*Under this heading will he included all Abstracts relating to the Histology 
of Diseased Tissues, both Animal and Vegetable. 
+Edin. Med. Jr., July, 1888. Boston M. and S. Jr., No. 8, 1889. 
