26 H. GOLDING BIRD. 
used it and seen it used with very many varieties of tissue, 
and never found it exert a pressure that in any way was 
productive of harm, and this remark applies even to such 
structures as spinal cord, provided they have previously 
undergone, as stated above, the usual amount of hardening. 
Should it be feared in any one case that pressure, however 
slight, might do some injury, the specimen can previously 
be covered with a thin coating of wax or paraffin, and then 
fitted into the pith. The chance of the pith revolving in the 
microtome like wax has already been alluded to; this in- 
convenience never occurs, the friction offered by the rough 
pith being sufficient to prevent it. To the vegetable 
histologist pith is an invaluable medium; for wax et hoc 
genus omne are almost out of the question when it comes to 
cutting sections of leaves and the like; while, further, the 
pith is far less likely to blunt the razor, and is more easily 
moulded than carrot, to which many resort for a similar 
purpose. 
It may further be urged that pith always involves the 
use of the microtome ; and so it certainly does: for when 
simply held in the fingers, though capital results may be 
obtained, I fully admit that imbedding in wax is preferable 
if the time for it can be spared. ‘The question, therefore, of 
pith versus wax is one chiefly of time and of comparison, 
and though many microscopists seem to have an innate 
hatred of microtomes, I ask whether it is better to adopt a 
process involving mechanical aid, but that costs no time to 
speak of, and next to no trouble, or one in which mechanical 
aid without special adaptation cannot, even if required, be 
employed, and in which time must be sacrificed in prepara- 
tory steps ; and, in consequence, much trouble given? It will 
be seen, of course, that [ am especially alluding to the rota- 
tion of the wax in the microtome, as well as to the fact 
that a tissue once imbedded in the machine cannot a second 
time be refitted without an entirely new process of casting. 
Such is not the case with pith. The specimen may be placed 
a score of times in the microtome, and after each be replaced 
in spirit, and as quickly refitted in the pith, if required, as 
on the first occasion. This suggests the combined use of 
pith and wax that may be employed; it has already been 
mentioned as protecting the specimen from all harm from 
pressure ; but it is useful also after a wax cast has been made 
in the microtome. Remove the wax when sufficient sections 
have been cut, pare the sides, and make it more or less 
square, and then, on the next occasion, pack it in a little 
pith, and it will be found to act as efficiently as at the 
