ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
545 
tion of spirit in the mixture, and at the end of eight or ten days place 
the tissue in pure spirit, and leave it until it is desired to examine it. 
A slice is then cut 3/16 to 1/16 in. in thickness, and placed for 
12-18 hours in absolute alcohol. It is then soaked in pure naphtha for 
24 hours. It is then placed in a mixture of equal parts of naphtha and 
soft paraffin, and exposed to a temperature of about 115° to 120° F. 
in a water-bath for 18-20 hours. The advantage of naphtha over 
turpentine is that it dissolves paraffin at a much lower temperature, 
thereby allowing the water-bath to be kept in such a condition that 
there is no danger of overheating the specimen. Throughout this 
process the temperature is kept lower than in the ordinary methods. 
The advantage of naphtha over chloroform and xylol is its cheapness. 
It is next placed in melted soft paraffin, and kept in the bath at about 
the temperature mentioned above for 24 hours. Then it is changed to a 
mixture of one part of soft and four or five parts of hard paraffin for 
the same length of time at a higher temperature. Care must be taken 
that the thermometer does not rise above 140° F. 
(2) Imbedding . — Paper on thin cardboard boxes, about 1 in. in 
depth, and slightly more than large enough to hold the tissue, may be 
used. Nearly fill with a warm melted mixture of soft and hard paraffin 
in the proportions already mentioned. This mixture is better than the 
hard paraffin alone. The sections do not curl up as they generally do 
when pure hard paraffin is used ; they can be cut in a much lower 
temperature, and they are not so brittle. With a pair of warmed 
forceps place the piece of tissue in the box, the face to be cut to be laid 
on the bottom. The paraffin should now almost fill the box wffiich is 
at once placed in a flat dish of cold water. This is an important step ; 
rapidly cooled paraffin makes a better bed, and is less apt to retain 
air-bubbles than the slowly cooled material. The boxes are removed 
from the water after a few hours, and can be kept until it is wished to 
cut them. 
(3) Cutting of Sections . — This should be done in a room only 
moderately warmed. The Bruce microtome is employed. Having 
removed the box from the block of paraffin, pare away the upper sur- 
face of the latter, keeping always parallel with the lower surface, until 
there is left only the thickness of 3/16 in. above the tissue. Then place 
this surface on the microtome plate, gently heating the latter until a 
thin layer of the paraffin melts. This is then allowed to cool, and the 
block becomes firmly attached to the plate. 
The plate is then screwed to the microtome, and the sections are cut 
in the usual manner. As the sections are thrown off they are caught in 
a dry tray. They may be mounted at once or preserved in boxes or 
bottles in a cool place. Some of the sections will be rolled up, others 
being wavy or flat. When the sections are very large, I prefer to 
mount the former ; they can be unrolled on the slide over a very gentle 
heat, without any wrinkling taking place, or without air-bubbles being 
caught beneath the tissue. 
(4) Mounting . — A clean dry slide is covered with a thin layer of 
fixing-fluid by means of a glass rod. The fluid which I have found 
most suitable is a mixture of collodion and clove oil. The section is 
flattened out on the slide by a soft hair brush above a very gentle flame. 
