370 ELDON W. SANFORD 
must be considered as derived from secretion or enzyme action 
of the crop. [If it is derived from a normal and usual acid- 
secretion flow, this secretion should be present after feeding of 
various foods. To test this a roach was fed a large amount of a 
paste of mineral oil, powdered sugar, and blue litmus powder, 
then the body cavity entered and a ligation made as before, 
and the animal left twenty-four hours before dissection. The 
experiment was thus exactly the same as the preceding except 
for the substitution of the indigestible mineral oil for the di- 
gestible olive oil. In this second specimen it was found on dis- 
section that the crop posterior to the ligation contained deep red 
material just as it did in the first specimen; but the crop anterior 
to the ligation was completely blue. We must now explain 
why acidity occurs in the crop-after olive-oil feeding, but not 
after mineral-oil feeding. All other possibilities having been 
ruled out, it seems that the acidity must have come from some 
product of the olive oil. This oil is neutral in reaction, but one 
of its digestive products is acid, namely, the fatty acid, in this 
case mainly oleic acid. This acid seems to me to be the only 
possible cause of the acidity observed, and if it is present it indi- 
cates that the fat (olive oil) has been split to its components in 
the crop and under the influence of the crop alone, other possible 
influences having been eliminated. The fat-splitting enzyme of 
the alimentary canal of animals is lipase. There seems good 
evidence that this lipase is secreted by the crop. Its purpose is 
to prepare the insoluble fats for use by changing or splitting 
them to soluble products, capable of diffusion. 
The real test of a digestive process consists in digestions car- 
ried on outside of the body. This method also allows quantita- 
tive calculations and affords an actual and true comparison of the 
digestive power of various organs. It also gives an opportunity 
to decide whether Petrunkevitch was right in asserting that the 
crop is the most important organ in fat digestion or whether it is 
a mere ‘subsidiary to the stomach, as so many authors have as- 
serted. Trials show that artificial digestions may readily be car- 
ried on. The test of the amount of digestion consists in titra- 
tion against alkali. When fat is digested fatty acid is produced, 
