PHYSIOLOGY OF DIGESTION IN BLATTIDAE 369 
the enzymes came all originally from the stomach, coeca, and 
salivary glands. 
My investigations indicate that the findings of the above in- 
vestigators are partially correct, but not entirely so. The cru- 
cial experiment was the following. An almost starved roach 
was fed a large amount of a mixture of olive oil, powdered sugar, 
and blue litmus powder. Immediately afterward the abdominal 
cavity was opened and the crop tightly ligated just anterior to 
the gizzard. The operation was done carefully and without much 
inconvenience to the animal. The parts were replaced in as 
nearly natural conditions as possible, and the animal was left for 
twenty-four hours, then dissected in salt solution. The colors 
of the contents of the various parts were observed to be as follows: 
crop anterior to ligation, red and some blue merging into red; 
crop at ligation, blue; crop posterior to ligation, deep red and a 
little blue merging into red. The redness of the crop posterior to 
the ligation indicated, no doubt, that acid secretion had migrated 
thence from the stomach and through the gizzard. The distinct 
blueness at the ligation point indicated that the ligation had 
been successful, for if it had not been, the acid secretion of the 
stomach would have flowed in through the gap and the color 
' would have been red instead of blue. The explanation of the 
redness anterior to the ligation is an interesting problem. Red- 
ness here means acidity, and the real question has to do with the 
origin of the acidity. Four explanations seems possible: 1) that 
some stomach secretion got into this part of the crop; 2) that the 
saliva from the salivary glands caused the acidity; 3) that the 
reaction of the food itself was acid, and 4) that the acidity was 
caused by the action of some secretion or enzyme of the crop 
itself. The first possibility need not be considered, for the tight 
and successful ligation, as mentioned above, prevented any flow 
from the stomach to this region. The second possibility is not 
valid, for all investigators hold that the saliva is alkaline or 
neutral. The third possibility is ruled out by the fact that some 
of the original paste was left in the feeding jar all through the 
experiment, and was as blue at the end as at the beginning. So 
the fourth possibility seems to be the true one, and the acidity 
