I 20 
Murphy— The Morphology and Cytology of the 
alcohol to xylol. This method of replacing the alcohol was used almost 
entirely, but accumulating experience has now led to the conclusion that 
it should be discarded. Successive mixtures of alcohol and xylol con¬ 
taining respectively 25, 50, and 75 per cent, of xylol were employed 
and the tissue was left about three hours or longer in each. A little eosin 
was added to the last mixture so as to stain the material red and facilitate 
embedding and trimming afterwards. Acid alcohol washes it out of the 
ribbon on the slide in a few seconds. The tissue was finally transferred to 
pure xylol and allowed to remain there until clear. 
The paraffin must be added gradually, a small piece at a time, first 
at room temperature and, when saturated, at the higher temperature of 
the oven top. Great care must be taken to prevent crystallization when 
the temperature drops at night. If the xylol is saturated at room tem¬ 
perature it may be kept overnight in the 25 0 incubator; or if it be on 
the oven top, it may be left in safety if covered with an inverted beaker. 
The whole process is troublesome and unsatisfactory. An attempt was 
made to devise a simple method of infiltration, and while some success 
was attained (and indeed the apparatus was used entirely in the latter part 
of this work with good results), it is not so automatic that it requires no 
attention or that it does not get out of order occasionally. The method 
consists in casting thin rods of paraffin in a glass tube, previously coated 
with glycerine, and inserting them through a hole in the stopper of the 
vial containing the tissue in xylol. The rod slips down as fast as that 
part of it which is in the liquid goes into solution. It is probable that the 
device can be improved. The best material was obtained when left about 
forty-eight hours, or preferably less, in the paraffin oven. During half that 
time the xylol was allowed to evaporate before transferring the tissue to 
pure melted paraffin, but this step does not now seem to be necessary, 
especially if the xylol be saturated at a fairly high temperature. The 
material was not embedded in the paraffin to which it was transferred 
from the xylol-paraffin mixture, but was passed into another bath of pure 
wax and allowed to remain there a few hours. The same grade of paraffin 
should be used all through : there is no advantage in saturating the xylol 
with a wax of lower melting-point and then transferring to a higher. Wax 
melting at 61 0 C. was used to a large extent; but it was afterwards found 
that the 58° C. grade cut equally well, and this was exclusively used in the 
later work. 
An account of how the data relating to the treatment of each lot of 
material was made and preserved may be useful. Every fixing was given 
a serial number, and this number, written with a soft pencil on a piece of 
paper about a centimetre square, was dropped into the fixing fluid with 
the material and carried with it until they were both embedded in the 
same cake of paraffin. The same number was given to a slip of paper, 
