46 NOTES ON 
very thick, and boiled; when cold, it should be 
well beaten, and stirred with a wooden spatula, 
which must be repeated every day, to prevent 
mildew on its surface, previously examining a 
portion with a magnifier, to ascertain if it con- 
tains any eels. If the weather be warm, a few 
days will be sufficient to produce them. When 
they are once obtained, their motion on the 
surface of the paste will prevent any cryptoga- 
meous growth, and it therefore requires no fur- 
ther attention. In like manner it will prevent 
its freezing in the winter. If the paste is too 
thin, they will creep up the sides. In this 
case, a portion of very thick paste must be 
added, to preserve them. When it is desirable 
to give them a fresh supply of food, 1t must not 
be put upon them; but they must be placed 
upon it. 
To prepare them for the microscope, take 
a few drops of clean water, and put a small 
portion of the paste containing the eels into it. 
After it has stood a minute or two, the eels may 
be taken out and placed under the microscope, 
freed from a considerable portion of foreign 
matter. 
It is advisable to have the sliders for con- 
taining these objects thin, so as to impede as 
