SUGGESTIONS FOR THE LABORATORY ASSISTANTS 



1. Supplies for students. Each student should be provided with a jar or 

 vessel having a tight cover filled with 4 per cent formaldehyde (40 c.c. com- 

 mercial formaldehyde plus 960 c.c. of water); one or two watch glasses; and 

 a piece of filter paper. The jar should be large enough to receive com- 

 fortably the animals used in the course. The student should keep these 

 materials in his locker or elsewhere. Each student will also need a wax- 

 bottomed dissecting pan and finger bowls with glass plates for covers. The 

 dissecting pans are made from low granite-ware pans. The wax used is cerosin 

 (a commercial product obtainable from dealers in laboratory supplies), blackened 

 by lampblack. 



2. Materials for students. Three frogs should be allowed for each student. 

 The student should be directed to keep these frogs in the jar of formaldehyde and 

 warned that he will not receive any others. One frog is for the general dissec- 

 tion; a second for the work on general physiology; and a third, injected, for the 

 circulatory system and nervous system. It is always necessary to admonish the 

 student repeatedly not to leave the animals out on the tables and not to allow 

 them to become dry. Of the other animals one specimen should be sufficient. 



3. Section on frog. Care should be taken that the slit made in the frog at 

 the end of the first laboratory exercise is through the skin only; if through 

 the muscles also the viscera will protrude through the opening and their rela- 

 tions will be distorted. It is usually advisable to warn against cutting the frog 

 in the median ventral line. 



4. Chemicals required. The following solutions and solids are required in 

 the course; they are required in the order named: 



a) Dilute acetic acid for the wiping reflex, about 10 per cent, 10 c.c. of pure 

 glacial acetic acid plus 90 c.c. distilled water. 



b) Powdered carmine. 



c) Artificial gastric juice: i to 2 grams of commercial pepsin, obtainable 

 from any drug house, in 100 c.c. of 0.4 per cent hydrochloric acid. 



d) 0.4 per cent hydrochloric acid, 4 c.c. of pure hydrochloric acid plus 

 996 c.c. distilled water. 



e) Neutral litmus solution can be made by boiling litmus paper, but should 

 preferably be purchased from dealers. 



/) Pancreatic lipase: dissolve one, to two grams of commercial pancreatin, 

 obtainable from drug houses, in 100 c.c. distilled water. Add enough sodium 

 carbonate to render very slightly alkaline. 



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