ATROPHY OF THE ORGANS OF THE LARVAL FROG. 157 



protein impermeable dialyzing thimble in which I c.c. of blood 

 serum, free from hemoglobin, plus 2 c.c. of 0.7 per cent. NaCl so- 

 lution had been placed. The thimble was suspended in 20 c.c. of 

 distilled water ; toluene added to both liquids within and without 

 the thimble and placed in a thermostat at 30 C. over night- 

 Similarly, tails from atrophying individuals were removed, and 

 treated as the normal tail was prepared. At the end of 16 hours, 

 the dialyzate in 2 c.c. amounts was boiled with three drops of 

 I per cent, solution of "Ninhydrin" for one minute. The con- 

 trol (non-atrophying, normal) gave negative results while the 

 atrophying tissue gave positive. Several duplicates gave similar 

 results. 



In interpreting this experiment, it maybe urged that atrophying 

 tissue digests more rapidly than normal tissue. To determine 

 this point the following experiment was performed. 



Experiment. Sixty grams, wet weight, obtained by using the 

 whole body of several non-metamorphosing individuals were 

 ground in sand and made up. to a 25 per cent, digest with toluene 

 water. A similar digest was prepared from involuting larvse. 

 The preparations were incubated for five days at 37 C. Twenty- 

 five cubic centimeter aliquots of the digests were pipetted into 

 50 c.c. tannic acid solution which was left to precipitate over 

 night. The preparation was diluted to 100 c.c. filtered and 50 

 c.c. aliquots were examined by the Kjeldahl process for total non- 

 protein nitrogen. Duplicates gave the following results: 



Control 1.07 gm. protein per 60 gm. tissue. 



Absorbing i .68 



For the Van Slyke gasometric method, tannic acid could not be 

 used to advantage as a protein precipitant; 50 c.c. of boiling 

 saturated solution of potassium sulphate was made; otherwise 

 the procedure was as before : 



Control no mm. NH2 nitrogen per 60 gm. tissue. 



Absorbing 76 " 



The formol-titration method gave: 



Control 117 mm. NHs nitrogen per 60 gm. tissue. 



Absorbing 95 



