244 BULLETIN OF THE UNIVERSITY OF WISCONSIN. 



pendent upon the degree of expansion of the epithelial mem- 

 brane. 



In the case of stretched membranes the tension has been in- 

 creased to a point where the cells have been torn asunder. The 

 cement substance, albuminous in character, has exuded and given 

 rise to dots or circular figures when exposed to the silver stain, 

 while larger ruptures appear as various-sized and shaped open- 

 ings between the cells. 



Mechanical force, when applied to freshly mounted specimens 

 in Canada balsam, would often cause separation of the cells. To 

 show the effect of mechanical force specimens which showed, 

 when first mounted in balsam, no openings, were subjected to va- 

 rious degrees of pressure. A certain relation between the dis- 

 tribution and number of the resultant interruptions and the 

 force with which the cover-glasses were weighted was found to 

 exist. The greater the weight the more numerous the openings, 

 and if the pressure was applied to any particular part of a cover- 

 glass a change in the shape of the cells would follow. This was 

 manifested by a straightening of the intercellular lines and the 

 appearance of numerous openings between the cells which ra- 

 diated more or less from the center where the weight was ap- 

 plied. 



When the epithelium was underlaid by adipose tissue, blood- 

 vessels or Pacinian corpuscles, or in other words, when the 

 epithelium was supported by an elastic pad, separation of the 

 cells did not take place. 



CONCLUSIONS. 



As the result of my investigations I am forced to conclude 

 that in the central tendon, suspensory ligament, omentum and 

 mesentery of the cat there are no pre-formed natural openings 

 commonly called stigmata and stomata. 



It is true that I frequently obtained figures which corre- 

 sponded with the usual description of these structures ; but, ow- 

 ing to their great irregularity of distribution, their equally great 

 diversity in size and shape, together with their mechanical pro- 

 duction, I am led to regard them as accidental formations. 



