INTERNAL EESTITUTIVE SECRETIONS 



295 



standpoint to this physiological theory, in which the villus of the 

 intestine is regarded as an inverted glandular organ of internal 

 secretion. He examined the intestinal villi of various vertebrates, 

 but up to the time of his death had only published his observations 

 on the small intestine of the fowl, which seemed to him the 

 clearest and most important. 



When examined in different phases of digestion the villi, he 

 says, may present two entirely 

 different aspects, according as they 

 are in the resting or in the actively 

 absorbing state. In the first case 

 all the epithelial cells of the villi 

 are regular, and approximately equal 

 in form and height, with nuclei 

 that are always at the same level, 

 i.e. toward the middle or inner 

 third of the cell, and protoplasm 

 that stains more intensely towards 

 the external free end, less intensely 

 towards the basal portion beneath 

 the nucleus (Fig. 94). 



During its functional work, the 

 villus looks quite different. "While 

 the stroma of adenoid tissue, mingled 

 with bundles of plain muscle cells, 

 preserves the form and dimensions 

 of the resting state, the epithelial 

 covering undergoes profound modi- 

 fications, which entirely alter the 

 aspect of the villus as a whole 

 (Fig. 95). During the first phase 

 two distinct cellular zones begin 

 to be differentiated : an outer, 

 granulated and readily stainable FIG. 94. vnius of small intestine of fowl. 



j i v -i Resting state. (P. Mingazzini.) c, striated 



zone, and an inner, hyaline, less 



granulated zone, which stains pale 



yellow with picric acid. In a 



more advanced phase of absorption, 



the inner zone grows out beyond 



the nucleus, which tends to a conspicuous lengthening of the 



cells, so that the nucleus is pushed into the outer third of the 



body of the cell. Finally, in a third phase, the hyaline portion 



gradually liquefies or vanishes by internal absorption, till at last 



only the outer zone of the epithelial cells is left, at the base of 



which the nucleus is found almost in contact with the basement 



membrane. 



As shown in the figure, different parts may be distinguished 



-vl 



border of epithelium ; nc, nuclei of 

 columnar epithelium ; I, leucocytes 

 scattered in cytoplasm of epithelium ; 

 ml basement membrane of epithelium ; 

 cv, adenoid.tissue of villus which also con- 

 tains muscle fibres ; vl, central lacteal. 



