OF MICROSCOPIC OBJECTS. 177 
the syringe. For this purpose we must procure small 
earthenware or tin pots of the size required, which will 
differ according to the kind of work to be done; and to each 
of these a loose lid should be adapted to protect it from 
dust, &c. These pots must be allowed to stand in a tin 
bath of water, under which a lamp or gas flame may be 
placed to keep the temperature sufficiently high to insure the 
perfect fluidity of the mixture. The tin bath is, perhaps, 
most convenient when made like a small shallow cistern; 
but some close it on the top to place the pots upon it, and 
alter the shape to their own convenience. 
8. We will now inquire into some of the materials which 
are needed in this operation; the first of which is size. 
This substance is often used in the form of glue, but it must 
be of the very best and most transparent kind. To make 
the liquid which is to receive the colours for the usual mode 
of injecting, take of this glue seven ounces, and pour upon 
it one quart of clean water; allow this to stand a few 
hours, and then boil gently until it is thoroughly dissolved, 
stirring with a wooden or glass rod during the process. 
Take all impurities from the surface, and strain through 
flannel or other fine medium. The weather affects this 
a little as to its stiffness when cold, but this must be 
counteracted by adding a little more glue if found too 
liquid. 
9. Instead of glue, gelatine is generally used, especially 
when the work to be accom)lished is of the finer kind. The 
proportions are very different in this case, one ounce of 
gelatine to about fourteen ounces of water being sufficient. 
This, like glue, must be soaked a few hours in a small part 
of the cold water, the remainder being boiled and added, 
when it must be stirred until dissolved. A good size may 
be made by boiling clean strips of parchment for awhile, 
and then straining the liquid whilst hot through flannel ; 
but when the injections are to be transparent, it is of the 
greatest importance that the size be as colourless as pos- 
sible. For this purpose good gelatine must be employed, 
N 
