CHAPTER VIII 



THE PERMEABILITY OF ORGANIC MEMBRANES OTHER 

 THAN PROTOPLASM 



A NUMBER of animal and vegetable membranes are now 

 known which exhibit to a greater or less degree the pheno- 

 menon of semi-permeability, and a few have been investi- 

 gated within recent years which disclose a remarkable 

 selective action towards substances in solution. 



These are of interest, not only in themselves, but also 

 because they afford macroscopic demonstrations of osmotic 

 phenomena. 



PERMEABILITY OF SOME ANIMAL MEMBRANES. 



One very simple experiment illustrative of these pheno- 

 mena consists in boiling a sausage. The animal membrane 

 which constitutes its covering is freely permeable to water, 

 but does not admit of the outward passage of salts at all 

 readily. The result is that, both on account of the osmotic 

 action of the salts inside and of the imbibitional intake of 

 water by the colloidal animal tissues, a stretching of the 

 membrane results to such a degree that bursting usually 

 occurs. If punctured before rupture of the membrane has 

 ensued, a quantity of liquid will, in the majority of cases, 

 be squirted out. 



The membranes of the egg of the common fowl were 

 also found by the author (1909, 2) to show features of 

 interest. Immediately against the shell lies a tough mem- 



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