128 PROTOPLASMIC ACTION AND NERVOUS ACTION 



the cell swells in hypotonic solution the thickness of the 

 hyaloplasm remains constant; apparently this thick- 

 ness is regulatively maintained by the transformation of 

 material derived from the internal protoplasm. Cham- 

 bers' observations on marine eggs show many interesting 

 instances of the formation of films at cut surfaces or at 

 the surfaces of protoplasmic fragments; regions where 

 the protoplasm is broken down by mechanical or other 

 injury soon become delimited by films bounding them 

 from the adjoining unaltered protoplasm.^ In the 

 formation of artificial vacuoles by the injection of 

 solutions into egg cells through micro-pipettes, films 

 with semi-permeable properties are formed about the 

 introduced droplets.^ The composition of the salt 

 solution is an important factor in the formation of such 

 vacuoles; Chambers has recently shown that pure solu- 

 tions of NaCl diffuse into the protoplasm without 

 forming films, while if sufficient CaClz is present, each 

 droplet of solution surrounds itself with a definite film 

 and forms a vacuole. A recent study by Seifriz^ of 

 the physical properties of protoplasm, as exhibited under 

 micro-dissection, gives many interesting details on film- 

 formation by living protoplasm under various con- 

 ditions. 



De Vries showed in 1885"^ that the normal vacuoles 

 of plant cells are surrounded by membranes having the 

 same osmotic properties as the plasma membranes 

 (those inclosing the entire protoplast). In his experi- 



^ Chambers, loc. cit. ' 



* Kite, loc. cit.; Chambers, Jour. Gen. Physiol., V (1922), 189. 



3 Seifriz, loc. cit. 



^Jahrb. wiss. Botanik, XVI (1885), 465. 



