THE FUNCTIONS OF THE DIGESTIVE ORGANS. 533 



absorption is to be regarded as a process which is no more complicated 

 than the formation of a secretion. In the latter case cells take away 

 certain substances from the blood, while in the former case other substances 

 are taken from the digesting mixture. Just as the cells of the gland show 

 a selective power, so also those of the intestine have the power of choosing 

 their material. In considering the action of ferments we emphasized their 

 specific action and suggested that this is due to the peculiar structure of 

 the ferment molecule. We can apply the same reasoning to the cells 

 themselves, and believe that they are specific in their entire construc- 

 tion, and similarly are merely able to take up substances having 

 particular atomic groupings in the molecule. Indeed, we cannot 

 abandon the thought that the cells of the intestine in a certain sense form 

 a secretion from the substances obtained from the food which they give 

 up on the other side of the intestinal wall. As the gland-cells take the raw 

 material from the blood for the formation of their specific secretion, and 

 then in a short time throw it off only to build up more of it, so here we 

 can imagine that the cells in the intestine carry on their work in a similar 

 manner, and acting together eventually give to the blood a homogeneous 

 material. Certain residues are taken up by the lymph where they are 

 carried first to the mesenteric glands, from thence to be gradually given 

 up for further metabolism. 



It would be absurd to consider absorption to be a result of an unknown 

 force, merely because we are at present without insight into the process. 

 It is not without interest in this connection to recall an example which 

 at first glance appeared to show strikingly an actual intelligence on 

 the part of unicellular organism, but which can be explained more 

 simply. We refer to the observation of Cienkowski. 1 He studied the 

 absorption of nourishment by the Vampyrella Spirogyrce. It is a micro- 

 scopically-small, naked, reddish-colored cell. This simple being, iri 

 which not even a nucleus is discernible, seeks out, among all the various 

 algse that are at hand, always a certain especial kind, and leaves untouched 

 all other varieties. When it has come in contact with the suitable kind of 

 Spirogyra, it places itself firmly next to the cell-wall, dissolves it and 

 sucks in the contents. We now know enough concerning the action of 

 ferments, however, to show that the fact that this kind of Vampyrella 

 feeds only upon' special algse is not so remarkable. It is quite certain 

 that the cell-wall is dissolved by means of a ferment. The ferments are 

 evidently capable of acting only upon a certain kind of alga. We mention 

 this example at this place especially to show how we should look upon the 

 active absorption of substances on the part of the cells. It may be merely 



1 Arch, mikroskop. Anat. 1, 203 (1865). Cited by Bunge in his Lehrbuch der Physi- 

 ologie des Menschen, Vol. II, p. 4 (1901). 



