152 GENERAL BIOLOGY 



To harden for making macroscopic sections across the 

 body., .wedge -the valves open, place in .1 per cent chromic 

 acid for a day or so. Wash in water and preserve in alcohol. 

 When ready, for sectioning remove the valves carefully, 

 place the body of the clam on a piece of cork or wax and 

 with a razor or brain knife make sections from | to \ inch 

 thick. 



Snail. If the edible snail (French or Roman snail) is used 

 it must be purchased from dealers. 



Frog. Any of the common frogs will do, though they 

 should be as large as possible. For the study of living 

 specimens in the winter, material must be obtained from 

 dealers unless it has been collected earlier and kept alive 

 in a tank. . If the animals are placed in a tank and kept in 

 a cool place in running water, or the water frequently changed, 

 and there is a platform or float on which they may rest, it 

 is possible to keep them alive all winter. During cold 

 weather food is not needed. To preserve, anesthetize with 

 ether or chloroform and place in 5 per cent formalin. Al- 

 cohol is not so good as a preservative for these forms. 



For demonstration of circulation in the web, narcotize 

 the frog with chloretone, place on a plate of glass and cover 

 body with damp cloth. Hold the toes spread apart with 

 bent pins held in place against the glass with masses of 

 putty or wax. 



To inject the bloodvessels for the study of the arterial 

 system proceed as follows: Anesthetize the frogs with 

 chloroform or ether (the latter leaves them in somewhat 

 better condition), remove a piece of the pectoral girdle from 

 over the heart, and remove the pericardium. With the 

 scissors cut a slit in the ventricle, insert the cannula through 

 the ventricle into the truncus arteriosus, and with a steady, 

 gentle pressure fill the arteries with the injection mass 



