junTCi^^^^^^^^ of Filamentous Algse for the Microscope. 363 
decomposable cell contents, and leave the object clean and trans- 
parent, while the Diatomaceae, after such treatment as boiling in 
acid, can be mounted in Canada balsam, by means of which they 
are presented in such a state that the finest sculpture of their 
siliceous epidermis can be observed, and they are at the same time 
held within a preservative substance which does not permit of their 
movement and consequent danger of fracture ; the Desmidiae and 
the filamentous Algse in general cannot be preserved so, and several 
means have been devised to keep them, all of which have been to a 
certain extent unsatisfactory. Besides, there are some Diatomaceae 
which grow in chains, as the Fragillaria, the frustules of which are 
united by means of a substance that will not bear the contact of 
acid necessary to remove the cell contents; and again there are 
others, as the Gomphonema, which are attached to submerged 
substances by means of a flexible stalk called a stipe, which would 
dissolve under the same circumstances. Such Diatomaceae have 
been generally merely placed in a cell formed of cement, or other 
suitable substance, and preserved in a preservative solution, con- 
sisting either of pure distilled water, or water containing creosote, 
camphor, or other substance possessing antiseptic properties. And 
the same plan has been followed with the filamentous Desmidias 
and other Algae, but such specimens become, after a short time, 
unsightly. It is true that the general outline is preserved, but the 
cell contents either contract or change in form and colour, so as to 
injure the appearance of the specimen, or the same effect is brought 
about by the coloured matter generally accompanying gatherings 
of such organisms. 
My plan then is essentially as follows: — Supposing I have a 
gathering consisting for the most part of a filamentous Desmid, as 
Desmidium Swartzii, which is a common species around New 
York city at certain periods of the year, I place a small quantity 
of it in a test tube, and pour over it, so as to about quarter fill the 
tube, a strong solution of the so-called " chloride of soda," which I 
prepare for the purpose in the following manner. Those, however, 
who have not the facilities for doing so, or do not desire to prepare 
their own solution, can use that sold by the apothecaries under 
the name of " Labarraque's Solution of Chloride of Soda," which is, 
however, rather weaker than it is best often to use. My solution 
I make by adding to the water a large excess of the common 
chloride of lime of the shops, which is fresh and has not stood for 
a time in an open vessel exposed to the air, by means of which 
much of it becomes decomposed and useless for this purpose. 
After stirring well, and then allowing such a mixture to stand for 
a short time, until all that will not dissolve falls to the bottom, 
I pour off the clear liquid, and add to it a concentrated solution of 
carbonate of soda, the common "washing soda," until the white 
VOL. I. 2 c 
