FROG. 



For an economical use of material this order may 

 be observed : 



For the first day's work follow sections I-III in- 

 clusive, and in YI the directions for exposing and 

 hardening the central nervous system. This frog 

 should then be put into formic aldehyde solution of 

 1 to 2 per cent., which is especially good for hard- 

 ening the nervous system. If the odor of the formic 

 aldehyde is unpleasant, the material may be rinsed 

 in dilute ammonia before being used. 



Taking a fresh frog on the second day, work out 

 upon it the circulatory and urino-genital systems, 

 sections IY and Y. This frog should be kept in 

 Wickersheimer's fluid, which preserves it in good 

 condition for the study of muscles, etc. 



After a few days the brain, etc., of the first frog 

 will have become sufficiently hardened, and the 

 work may proceed in regular sequence. The direc- 

 tions after YI may be worked out upon either frog, 

 as the material serves. 



For this work on the frog it is sufficient to use a 

 water solution containing from 1 to 2 per cent, of 

 formic aldehyde. "Formalin" is properly a com- 

 mercial name for a 40 per cent, solution of formic 



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