PHYSIOLOGY .OF DIGESTION IN BLATTIDAE 393 
sticky mass in the lumen. This mass was called chyme; it often 
contained cells which exactly resembled leucocytes. These cells 
seem to devour fat and other foods. 
Schliiter employed methods somewhat similar to those of 
Petrunkevitch, but has disagreed with him in almost all the de- 
tails described. He is unable to find any evidence of absorbed 
‘fat in the epithelial or tracheal end cells. I have carefully ex- 
amined the data of his experiments which he has published, and 
I find that the time intervals he used were so chosen that only 
in a very few cases would absorption probably be in evidence. 
In only two of his experiments as given would significant ab- 
sorption be expected, judging from my results. These two 
experiments apparently represented single animals, so it seems 
that the chance individual variation of a very few animals 
from the usual absorptive function really explains Schliiter’s 
denial of absorption in the epithelial and tracheal end cells. 
Schliiter assumed that appearances of fat and chyme in tracheal 
tubes indicated a chance pushing or slipping of substance from 
other regions into the tracheae during sectioning of the material 
or preparation of the slide. Or the contents of the tubes may 
have entered them by capillary action during dissection. 
Schliiter’s final objection is that as such appearances have no 
reason nor physiological explanation, they have no actuality. 
In my first experiments I found stages which corresponded very 
closely with those of Petrunkevitch. I used animals which had 
been starved two weeks and fed them a paste of olive oil and 
pulverized sugar. The animals were removed after certain in- 
tervals and dissected, immersed in normal salt solution. The 
crop was slit longitudinally so that the contained food might 
float out, the tracheal trunks of the crop were cut and the crop 
was removed and placed in Flemming’s fluid. Flat mounts of 
the wall of the crop were made and also paraffin sections. Such 
preparations revealed the presence of black fat in the tracheal 
tubes, either in some of the smaller tracheae or in both large and 
small tracheae. The pictures corresponded so closely with 
those of Petrunkevitch that I believed I had verified his work, 
and I so stated in a preliminary paper. 
