PHYSIOLOGY OF DIGESTION IN BLATTIDAE oie 
and the amount of acidity present at any stage depends on the 
fatty acid present, and is a measure of the extent to which fat has 
been split, or, in other words, how far its digestion has proceeded. 
Thirty animals were used in the crucial experiment. They had 
been starved for varying periods, so that little food was present 
in the crops or stomachs. All receptacles used were cleaned by 
boiling at the beginning of the experiment and physiological pre- 
cautions were observed. ‘The animals were all carefully dissected, 
the crops and stomachs removed, the crops put into one dish of 
normal salt solution, and the stomachs with their coeca into an- 
other. After the salivary glands were removed, the crops were 
sht longitudinally, and the contents carefully washed out with a 
soft brush. The thirty crops were rinsed and ground to a pulp 
in a mortar, 30 ec. of normal saline being added. This was left 
for two hours while the enzyme was extracted, then the solid 
matter was removed by filtration. The filtrate (about 25 ec.) 
was made up to 30 ee. with saline and divided to three portions 
of 10 ce. each in flasks. One portion was titrated at once 
against 1/20 normal NaOH, using phenolphthaleine as an indi- 
cator, and found to be neutral. The flask containing another 
portion of 10 ec. was plugged and left three days at room tem- 
perature in darkness, then titrated. This showed an acidity 
corresponding to 0.1 cc. of the alkali. This slight increase in 
acidity over the original amount was due to bacterial or o her 
causes. To the third flask of 10 ce. of the extract was added 10 
ee. of pure olive oil (neutral by titration tests), the mixture was 
left three days in darkness at room temperature and shaken at 
intervals. It then showed by-titration an acidity corresponding 
to 10.8 ec. of 1/20 normal alkali.-- Comparing the flasks with and 
without olive oil, there has been an increase in acidity corre- 
sponding to 10.7 cc. of alkali. The two flasks contained the 
same amount of the same extract, and were treated similarly, 
but for the addition of the oil to one. Thus the acidity must 
have been derived from the olive oil, and must represent the 
presence of fatty'acid as a product of the oil. The presence of 
fatty acid indicated that splitting of the fat had occurred during 
the experiment, or, in other words, that digestion of the fat had 
