142 ORGANS AND ORGAN SYSTEMS 



finally, is constricted at each dissepiment so that its structure 

 follows the general metamerism of the body. 



The digestive fluid secreted by the wall cells of the intestine 

 corresponds in its essential features with the pancreatic juice 

 of mammals. Free acids cannot be detected in the gut, 

 where the fluids in general show -a slightly alkaline reaction. 

 According to Lesser and Taschenberg, albumin is broken down 

 under action of this digestive fluid in 3 1/2 hours at 37 C. 

 if the medium is slightly alkaline, and in 28 1/2 hours if it is 

 slightly acid. According to Abderhalden and Heise, a pep- 

 togenic ferment is also present, which accounts for the slow 

 digestion in an acid medium. The same observers also ex- 

 tracted an amylolytic ferment which 

 changes starch into sugar (maltose), 

 and found traces of a fat emulsify- 

 ing ferment. 



The digestive ferments are se- 

 creted by gland cells distributed 

 among absorbing cells of the gut 

 epithelium (Fig. 56). In prepared 



seetions ' the y ma 7 be distinctl y made 



enlarged gland cells with se- out, if filled With granules which 

 cretions. and between them, , ,, , , ... 



the absorptive cells. (From have an albuminous nature, but if 

 K. C. Schneider.) emptied of 'granules, they become so 



small and compressed that they are difficult to find. 



The absorption cells are columnar, ciliated, epithelial cells, 

 somewhat broader at the ciliated end. In each there is a 

 typical and characteristic closing apparatus. The free sur- 

 face possesses a cuticle-like covering which bears a hedge of 

 fine, stiff rods, through which the cilia pass from their basal 

 bodies in the cell to the lumen of the gut. These cilia are 

 absent on the cells of the typhlosole, where fat absorption is the 

 chief role (Greenwood). The function of the minute rods'is un- 

 known but they occur very generally on absorption cells. 

 Granules of absorbed food-stuffs are often visible in these cells, 

 some of which may be recognized. Thus, if powdered carmine 

 or indigo is mixed with the worm's food, the colored granules 



