THE FROG 



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 individual 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 move- 

 ments use the frogs in the cages. 



IV. KILLING AND PRESERVING. 



As a 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; also it is less expensive. Place the frogs in an air- 

 tight glass jar containing a liberal quantity of cotton sat- 

 urated with the anaesthetic. In case it is desired to dissect 

 the freshly-killed specimens, the frogs should be anaes- 

 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 anaesthetized for a shorter 

 time they may become active during dissection, an occurrence 

 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 killed by drowning or asphyxiation in an 

 air-tight jar, but this requires considerable time. 



In case the frogs are to be preserved immediately after 

 anaesthetizing, an incision should be made through the skin 

 and abdominal wall, a little to one side of the median line, 

 to admit the preserving fluid to the body cavity. 



In special cases it may be advantageous to kill the frog 

 by an operation known as " pithing." With the finger-nail 



