62 THE FROG 
Ernst Leitz, 30 E. 18th St., New York. (Microscopes and accessories.) 
Bausch & Lomb Optical Co., Rochester, N. Y. (Microscopes and acces- 
sories; dissecting instruments.) 
Spencer Lens Co., Buffalo, N. Y. (Microscopes and accessories; dissecting 
instruments. ) 
TII. Care oF Livinc MATERIAL. 
Live frogs may be kept in a tank containing one or two inches 
of water. Frogs in captivity often die from the attacks of 
parasites; loss from this source may be minimized by frequently 
cleaning the tank and changing the water, also by keeping only a 
small number of frogs in a single tank. If kept in a cool place, 
frogs do not require food during the winter season. 
In the laboratory a few frogs may be kept for observation and 
experiment in small cages supplied with water. Insect cages are 
excellent for this purpose; they should open at the top. For 
studying the swimming and diving movements a few small frogs 
may be placed in battery jars nearly full of water; if the water 
is warm the frogs will not stay long at the bottom. For in- 
dividual work on the living frog each student should be supplied 
with a specimen covered with a finger-bowl inverted over a glass 
plate (one frog is sufficient for two students). The students 
should be cautioned not to allow the frogs to escape; for studying 
the leaping movements use the frogs in the cages. 
IV. KiLLING AND PRESERVING. 
Asa rule it is best to kill the frogs with sulphuric ether or with 
chloroform. Ether has some advantages over chloroform in that 
it leaves the specimens limp instead of rigid, and to most persons 
the odor of ether is not so unpleasant as that of chloroform. 
Place the frogs in an air-tight glass jar containing a liberal quan- 
tity of cotton saturated with the anesthetic. In case it is desired 
to dissect the freshly-killed specimens, the frogs should be anes- 
thetized at least one hour before they are needed; in such frogs, 
after a time the heart will usually resume its beating, as is 
desirable. If the frogs are anesthetized for a shorter time they 
may become active during dissection, a circumstance which is 
very disconcerting to both student and teacher. If it is not 
desired to demonstrate the action of the heart, the frogs may be 
