OF INSECTIVOROUS PLANTS 433 



of 6 hours; in these experiments Nessler's reagent was used for the 

 colorimetric determination of ammonia. 



Pieces of meat, the size of grains of rye, were introduced into pitchers; 

 after 2 days, the contents of 3 pitchers were acid in reaction, those of 

 5 pitchers neutral in reaction; after another week had passed, the con- 

 tents of but 1 pitcher had an acid reaction which, however, was not very 

 marked. 



A vigorous plant of Nepenthes paradisiaca was cultivated in a glass 

 chamber at a temperature of 20° to 25° C. in an atmosphere saturated 

 with moisture. The plant bore 3 pitchers. The oldest of the pitchers 

 was brownish and no longer vigorous, and contained a small amount of 

 neutral liquor. A wasp was introduced into the liquor and soon died; 

 3 days later the liquor had an alkaline reaction; bacteria and infusoria 

 were present in abundance. The second pitcher contained an acid 

 liquor, in which a small fly was present. This liquor dissolved fibrin 

 (which had been stored in glycerol, washed, and strongly swollen) in 1 

 hour; after 3 hours, soluble protein was absent, but peptone was present; 

 the temperature of incubation was 25° C. Another fibrin flock and 0.2 

 percent hydrochloric acid were added, and the temperature of incubation 

 was changed to 16° to 18° C; the flock dissolved in 40 minutes; this solu- 

 tion was sown on nutrient gelatin, and bacteria were not found. 



The youngest pitcher was still closed. Inoculation of its contents 

 into nutrient gelatin gave no growth. The liquor was neutral in reaction 

 and mucilaginous. A flock of swollen fibrin and 0.1 percent formic acid 

 were added to the liquor; the flock was completely digested in 12 hours; 

 even after 8 days, bacteria were absent as was shown by a nutrient gelatin 

 culture, which was made in duplicate. It was also found that 0.1 percent 

 formic acid prevented the development of putrefactive bacteria in an 

 approximately 0.5 percent peptone solution, which was exposed in the 

 open air for 8 days, and that only a few mold-threads developed. When 

 the acid had not been added to the peptone solution, clouding and an 

 unpleasant odor soon appeared, due to the development of innumerable 

 bacteria. 



Goebel interprets these observations: — 



" These facts in themselves suffice to refute the acceptance of a bacterial 

 digestion. They show that, in the Nepenthes hybrid studied, even in 

 the unopened pitcher, a peptonizing enzyme is present which exerts an 

 energetic digestive action on the addition of acid. Normal pitchers, 

 into which an insect falls, very soon secrete formic acid. With excessive 

 feeding, of course, the enzyme action is insufficient and putrefaction 



