THE COLLOIDAL STATE 119 



molecule are the bases of the unique behavior of colloidal systems. 

 The micelle satisfies these qualifications, for it is an aggregate of 

 molecules and below microscopic visibility. When a molecule 

 (such as those of proteins) is large enough to present an 

 appreciable surface, then it will qualify colloidally as well as does 

 a micelle. 



Biological Applications. — Protoplasm, in its coarser microscopic 

 structure, is a suspension of minute particles; it is, therefore, a 

 suspension (lyophobic) colloid. The matrix or dispersion 

 medium (continuous phase) of this suspension contains gel- 

 forming substances (albumin, etc.) which impart to protoplasm 

 the properties of gels or jellies. These substances and their 

 properties are believed to be more fundamental in life than the 

 superficial and microscopically visible colloidal suspensions; 

 however, both play their part, both are necessary to the vital 

 activities of protoplasm. 



The colloidal state of protoplasm will be considered again and 

 again in this book. We may here add one application of the 

 suspension colloids in medicine. This is in the field of anti- 

 septics. Heavy metals, such as copper and mercury, are highly 

 toxic. Colloidal preparations of metals, particularly silver, 

 dispersed in water or oil or prepared in dry form to be later 

 dispersed by the user, have come into extensive use as antisep- 

 tics. Good results are claimed for colloidal silver in the treatment 

 of throat, nose, and sinus inflammation and in bladder troubles 

 (cystitis), but the curative powers may in many cases be purely 

 palliative. Assuming that the beneficial results are due to the 

 germicidal action of the solution, upon what do these peculiar 

 properties rest? The high toxicity of heavy metals suggests 

 that the metal itself is the agent. Freundlich and Sollner found 

 that colloidal silver is taken out of suspension and deposited 

 within algae. They believe this to be the explanation of the 

 oligodynamic effect which Nageli obtained for copper (page 428). 

 Precipitation of the bacteria by neutralization of their electric 

 charge is not a satisfactory interpretation of the toxic effect of 

 colloidal metals, as both silver and bacteria are negative in sign. 

 While it is possible that the metallic solution may owe its germi- 

 cidal qualities to the toxic effect of salts of the metal, it is also 

 possible that instead of the metal being deposited within the 

 cells, the bacteria are coated, literally plated, with a layer of 



