PHYSIOLOGICAL ABSORPTION. 335 



of the crypt, and push the new cells upwards. The cells 

 themselves are pliant, easily accommodating their shape to 

 the changes of that of the villus wrought by its specific 

 muscle, and possess at their free border the well-known 

 " basal band " {basqlsaum) of Kolliker, with the " rodlet 

 organ " {stabchenorgaii) of Brettauer and Steinach. 



This organ to which so much attention has been de- 

 voted is, according to Heidenhain, composed of a number of 

 minute rods in intimate connection with the cell protoplasm 

 and imbedded in a somewhat softer material. The rods 

 can be retracted into the cell, and are also capable of con- 

 siderable extension beyond it, becoming hair-like, a condi- 

 tion most easily brought about by direct excitation of the 

 surface either chemically or mechanically {e.g., by tape- worms 

 in the gut). As confirmatory of this idea of the rodlet organ 

 must be mentioned the recent work of Miss Greenwood, who 

 in the earth-worm saw appearances suggestive of " retractile 

 cilia " in the gut cells, those cells which are loaded with 

 nutriment having retracted cilia, while those devoid of food 

 stuffs have their cilia extended. Brettauer and Steinach, 

 indeed, thought that the rods were present in the basal band 

 during hunger but absent during digestion. 



Thanhoffer, too, has maintained that in the frog, especi- 

 ally when the mucosa is wetted with bile, processes extend 

 from the basal band in the fasting state, and Wiedersheim 

 maintains the existence of a similar state of affairs in the 

 gut of the amphibian Spelerpes fuscus. The swallowing of 

 food particles by means of pseudopodial processes in the 

 digestive cells of certain lower Metazoa is known to us 

 through the researches of Metschinkoff upon intracellular 

 digestion, and Wiedersheim admits the possibility of some 

 such action in vertebrates, though the ancestral method is 

 modified, in that by the substitution of extra- for intra- 

 cellular digestion the cells will only take up matter that has 

 been especially elaborated for them by the digestive fer- 

 ments. These observations, especially those of Thanhoffer 

 in the frog, urgently need repetition. 



The epithelium then of the villus is highly specialised, 

 and, as far as the passage of fluid from the gut to the 



