58 PROTOPLASMIC ACTION AND NERVOUS ACTION 



are prevented by the pervading film-structure from fusing 

 or otherwise losing their identity — undergo alteration or 

 breakdown; a general coarsening or increase of opacity, 

 indicating coagulative changes in the cell proteins, is 

 characteristic of dying protoplasm, and is associated with 

 the changes in mechanical properties described above.^ 



The basis of these changes is insufficiently understood 

 at present, but their ready production by lipoid-solvent 

 compounds seems to indicate that the lipoid constituents 

 of the protoplasm are specially involved. Apparently 

 the Hpoids have a relation to the protein constituents 

 resembling that which a '^protective colloid" (gelatine) 

 added to a suspensoid hydrosol (gold) has to the colloidal 

 particles of the suspensoid. In the presence of the 

 protective substance the particles remain separate under 

 conditions, such as the presence of salts or increase of 

 H-ion concentration, which otherwise lead to fusion or 

 precipitation;^ this stabilizing influence is apparently 

 dependent on the formation of thin adsorption films 

 about the particles. In the case of living protoplasm, 

 the evidence from cytolysis and similar phenomena 

 indicates that the normal fine subdivision of the struc- 

 tural proteins — shown by the characteristic translucency 

 during life — is dependent on the presence of thin lipoid 

 films (possibly soap) at the surface of the protein particles, 

 fibrils, or other structural elements. When these films 

 are broken down or destroyed, a coalescence of particles 

 and a coarsening of structure result; these effects involve 

 a loss of semi-permeability, together with the changes 



^ The progress of structural changes of this kind can be followed by 

 the microscope under dark ground illumination; cf. Aggazzotti, Z. allg. 

 Physiol., XI (1910), 249. 



* Zsigmondy, Colloids and UUramicroscopy. 



