1897] BRIEFER ARTICLES 373 
practical knowledge of methods which is especially useful to those who 
are looking forward to teaching in the secondary schools. 
The method is, in brief, to carry the material through all the pro- 
cesses of fixing, dehydration, and infiltration, with some medium in 
which the sections can be made and have the material ready to section 
at a moment’s notice: not simply to prepare enough material for the 
use of the class of one year, but to prepare a sufficient quantity at once 
to meet the wants of a class of ten to twenty students for a period of 
years. ‘Take for example, among the bryophytes, such liverworts as 
Riccia, Marchantia, Preissia, Pellia, Pallavacinia, Ptilidium, Cephalozia, 
etc. To obtain material for classes in several stages of development 
takes a considerable amount of time. When the material is once 
found in quantity it requires but little more time to carry through a 
large amount which will last for a period of years than to prepare just 
enough for one year. And this is the principle which I have adopted 
in the preservation of material for class study. The greater amount 
of material has thus far been prepared by the collodion method, and 
when once imbedded in collodion the blocks containing the plant 
parts ready for sectioning are stored in 80 per cent. alcohol, and then 
are ready to cut on a moment’s notice and to serve to the class. For 
certain material collodion is excellently adapted, while for other 
material it is poorly adapted, and I have been obliged in many cases 
to resort to paraffin imbedding, which is far superior for certain kinds 
of work. 
It is unnecessary to give here in detail the processes of fixation, 
dehydration, and infiltration in collodion. These are sufficiently well 
known or can be obtained from the books. But it may not be amiss 
to give briefly the method which I have recently adopted with success 
in imbedding large quantities of material at one time in collodion. I 
use collodion made by dissolving ordinary gun cotton in equal parts 
of 95 per cent. alcohol and ether; two solutions, a thin one of 2 per 
fent. Consistency (2 grams gun cotton to 100” alcohol and ether), and 
2 thicker one of 5 per cent. consistency. 
The objects are previously trimmed to the desired size and form 
for sectioning. From the vial which holds them the 95 per cent. alco- 
hol is decanted, and if there is considerable bulk of tissue an amount 
of ether approximately equal to the estimated amount of alcohol 
remaining in the tissues is added before pouring on the 2 per cent. 
collodion. This prevents an excess of alcohol which flows out of the 
