242 COLLOIDS IN BIOLOGY AND MEDICINE 



not exclude RUHLAND'S ultrafilter theory. If we have an emulsion 

 in which the lipoid is the dispersed phase we have an ultra filter which 

 is permeable for water soluble substances and impermeable for lipoid 

 soluble substances. The size of the pores of the ultra filter depends 

 on the relation of the lipoid to the aqueous phase. If the amount of 

 lipoid is small, the pores of the ultra filter are large and vice versa. 

 When the lipoid content is large we have a narrow pored ultra filter 

 which absolutely satisfies the conditions found by RUHLAND in his 

 dye investigations. Further, we have seen from CLOWES' experiment, 

 that an oil/water emulsion is easily changed to a water/oil emulsion, 

 and in that case the layer is open for fat soluble substances and closed 

 for water soluble substances In my opinion such a layer satisfies 

 all the conditions demanded by the various investigators. 



I wish, however, to emphasize that there is no justification for too 

 wide a generalization, for different cells behave very differently. 

 Observations on plant cells cannot be applied without modification 

 to animal cells; a cell in a plant root cannot be compared to nerve 

 cells which are surrounded by a dense isolating layer of fat. It seems 

 possible to conclude from R. HOBER'S and RUHLAND'S experiments 

 on the penetration of dyes into cells that the animal cells which they 

 studied contain larger pores than the plant cells. 



Let us consider the simplest instance, one in which the cell proto- 

 plasm is a colloid capable of swelling, with surfaces limited by a 

 pellicle which can also swell and offering certain exterior boundaries. 

 Any injury to this pellicle will be repaired of its own accord somewhat 

 like rubber. We can thus (pp. 284-285) readily understand how 

 amcebce or phagocytes send out protoplasmal prolongations, envelop 

 foreign bodies or bacteria and incorporate them without their margin 

 being broken. As a matter of fact, it must immediately repair itself 

 just as does an oily film on water broken by a stone. Let us see how 

 this view agrees with former theories, and to what extent this view is 

 an improvement upon them. 



To begin with, it must be noted that OVERTON assumes that a sub- 

 stance is taken up by the plasma pellicle in accordance with its 

 coefficient of solubility, in agreement with the laws of solutions 

 (HENRY'S distribution). This may be the fact in many cases, only we 

 must recall that adsorption fulfills similar conditions for the passage 

 of a substance through the plasma pellicle into the interior of the 

 cell. The only condition which need be assumed in order that a 

 substance may enter the interior of a cell from outside, is that there 

 shall be a reversible absorption by the plasma film. What curve of 

 distribution this follows, is immaterial for the present. That, as a 

 matter of fact, in numerous cases an adsorption certainly does exist, 



