and Laboratory Methods. 2321 



The Technique of Biological Projection and Anesthesia of 



Animals. 



Copyrighted. 



XIV. THE ANESTHESIA OF ANIMALS.— Concluded. 



Vertebrata : Frogs. — These common animals have long been used in 

 exhibiting that instructive and classic experiment of all physiology courses, the 

 circulation of the blood. Frogs for this purpose have been kept quiet in vari- 

 ous ways, including anesthesia with chloroform, pithing, injection of curare, 

 wrapping the animal in moist cloth, binding it on a frog-plate or on a thin 

 board, the webs being stretched by pinning out or by cords looped on the toes, 

 and by other more or less successful methods which usually either finally kill 

 the frog or cause it constant suffering. The chloretone method is an improve- 

 ment on all of the above. It is reasonably rapid in its action, requires little 

 apparatus, interferes less than any other with the normal circulation, gives an 

 absolutely quiet frog for study, and the frog usually recovers completely from the 

 anesthetic and may be used repeatedly. 



To anesthetize a frog with chloretone take about 1 c. c. or 25 to 30 drops of 

 a 1 per cent, solution in a small, smooth-tipped pipette with a rubber bulb, /. e., 

 a straight medicine dropper, or a fountain pen filler, and inject the solution into 

 the animal's stomach by inserting the point of the pipette into the animal's mouth 

 and pushing it well down into its esophagus. Press slowly and steadily on the 

 pipette bulb and force the liquid into the frog's stomach. The only difficulty is 

 in holding the frog and opening its mouth ; but this is an easy matter if per- 

 formed as follows : Grasp the frog's hind legs with your right hand, place the 

 frog's back across the palm of your left hand, with its head projecting above 

 your thumb and first finger, and your little finger holding the frog's hind legs, 

 when your hand is closed over the animal. A slight pull on the lower jaw is 

 sufficient to open the mouth, which may be held open with the first finger, or 

 with a gag made of a match pushed well back between the open jaws and ex- 

 tending beyond the jaws on either side. The point of the pipette should be car- 

 ried well down into the esophagus so as to insure the entrance of the anesthetic 

 into the frog's stomach. Medium and large frogs require a second and third 

 dose of 1 c. c. each, which may be given at intervals of three to five minutes 

 after the first dose. 



The frog becomes as perfectly passive as it would be if it were dead. Care- 

 ful studies of the eyes, nostrils, ears, mouth, tongue, eustachian tubes, esopha- 

 gus, glottis and other parts are easily made, or the frog may be mounted on the 

 microscope for the study of the circulation of the blood in the web of the foot. 

 This is best done by taking a plate of glass, about four by five inches in size, 

 and placing it on the stage of the microscope, where it is held in place by the 

 stage clips. The anesthetized frog is placed in its normal sitting posture on the 

 glass plate a little to one side on the objective and one hind foot is pulled far 



