1892,] Microscopy. 971 
worked up regions by far the larger portion of the Micro-Hymenop- 
tera and Micro-Diptera remain absolutely undescribed in our collec- 
tions, and have been but very partially collected, it will be safe to 
estimate that not one-fifth of the species extant have yet been charac- 
terized or enumerated. In this view of the case the species in our 
collections, whether described or undescribed, do not represent perhaps 
more than one-fifth of the whole. In other words, to say that there 
are 10,000,000 species of insects in the world, would be, in my judg- 
ment, a moderate estimate.” 
MICROSCOPY.’ 
Gulland’s Method of Fixing Paraffine Sections to the 
Slide.’—A fter pointing out the difficulties arising from the use of the 
albumen fixative the author offers the following method : 
The tissue isimbedded in the usual manner. In trimming the block 
for sectioning, care must be taken to see that the surface meeting the 
_razor is exactly parallel to the opposite surface ; these surfaces are then 
coated with soft paraffine, and when this has hardened are again 
trimmed square. The reason for this special care is that any curve in 
the ribbon produced by neglect of this precaution is accentuated by 
the later flattening of the sections. When all the sections required 
have been cut the ribbon is divided into lengths corresponding to that 
of the cover glass in use. 
A flat glass dish filled with warm water is now provided ; the tem- 
perature should never be high enough to melt the soft paraffine hold- 
ing the sections together. Short of this, however, the warmer the 
water the more rapidly and completely are the sections flattened. 
The ribbons are seized at one end with forceps while the other end 
is gently lowered upon the surface of the warm water ; as the sections 
flatten out they will move along the surface of the water; when the 
flattening is complete the slide, carefully cleaned, is immersed in the 
water. The ribbon is floated into its position with a stiff brush; this 
process is repeated until the slide is full, when it is set up on end until 
the water is thoroughly drained off. The slide is then transferred to 
the top of the imbedding oven, where the temperature is a little under 
50° C., and where, consequently, the paraffine of the sections is not 
1This department is edited by C. O. Whitman, Chicago University. 
Jour. of Anat. and Physiol., Vol. xxvi. 
