148 



GENERAL PHYSIOLOGY 



runs away. A second rare case of this kind is afforded by Vavipy- 

 rella Spirogyrce. The amoeba of this species applies itself to a 

 healthy Spirogyra, bores through the cell-wall and devours the 

 slowly escaping primordial utricle together with the chlorophyll-^ 

 bands. It seems to be able to satisfy its hunger upon Spirogyra 

 only." (Fig. 48.) 



But we need not search so far. In the human body there are cells 

 that behave similarly. As Metschnikoff ('92) has shown by his 

 researches extending over many years, the leucocytes or white 

 blood-corpuscles, the amoeboid wandering-cells, devour and digest 

 certain forms of bacteria present in the body, while they scorn 

 and even directly avoid other bacteria; likewise, intestinal 



Fig. 48 — Vam'pyrella Spirogyne boring into and suck- 

 ing out a Spirogyra-ce^. A. The Spirogyra-ceM is 

 pierced and the contents are passing out into the 

 VaiiipyreUa. B. The Spirogyra-QoW is completely 

 emptied. At * a ceU that has been pierced and 

 emptied. (After Cienkowski.) 



epithelium-cells, as has been seen, devour only fat-droplets, while 

 they behave wholly passively toward other small particles that are 

 brought into the intestine, such as granules of carmine. 



Finally, another very interesting phenomenon, which has to do 

 with the ingestion, not of food, but of substances that likewise 

 play a rdle in the life of the organisms in question, has also 

 frequently been referred to, although incorrectly, as a power of 

 selection on the part of the cell. This is the ingestion of material 

 for shells and capsules on the part of certain shell-bearing 

 rhizopods. The Difflugice, which are unicellular fresh-water 

 Bhizopoda whose naked protoplasmic bodies are fixed in a very 

 delicate urn-shaped or flask-shaped capsule, take up the material 

 for their tiny dwellings with their finger-like pseudopodia out of 

 the mud of the pools and lakes at the bottom of which they live.i 

 The structural material of their shells is very varied, but in many 



I ('/. VerMui'ii CSS). 



