294 PROPERTIES CONFERRED BY COLLOIDAL CONSTITUENTS 



Hence if tadpoles, anesthetized at 30 by a 2 f solution of Chloral 

 Hydrate be cooled they recover their mobility, on warming they are 

 again anesthetized, and at 30 the solubility of chloral hydrate in olive 

 oil is much greater than it is at lower temperatures. 



While the inference drawn by Overton and Meyer from these experi- 

 ments, that only those substances which are soluble in Lipoids can 

 penetrate the cell, obviously cannot be substantiated, for otherwise 

 neither water, inorganic salts nor amino-acids could ever gain entry into 

 protoplasm, yet it is very manifest from these and many other experi- 

 ments of a like nature that substances which are soluble in lipoids do 

 enter living cells with exceptional ease. We may probably infer with 

 safety that the lipoidal elements in the superficial membranes of cells 

 constitute a large proportion of the surface, and the interstices a rela- 

 tively small proportion, so that substances which are insoluble in lipoids 

 enter living cells with comparative difficulty 



FIG. 17. Illustrating the increase in the diameter of the interstitial spaces which results 

 from increase in the diameter of the fat-droplets in an emulsion. 



Any reagent or condition which affects the State of Aggregation 

 of the fat-globules in the limiting membrane of cells must necessarily 

 affect the diameter of the interstices between them. In general those 

 conditions involving the formation of large aggregates would increase 

 the permeability of tissue by enlarging the diameter of the radiating 

 fat-droplets and, therefore, that of the interstitial spaces (Fig. 17). 

 This is very strikingly illustrated by the eggs of certain marine forms 

 such as the sea-urchin which, when exposed to the action of fat-solvents 

 become permeable to water which they take up from the surrounding 

 sea-water. The water thus absorbed accumulates in a layer just under 

 the superficial membrane of the cell, lifting it off the underlying pro- 

 toplasm and forming the "Fertilization Membrane" which is normally 

 the effect of a cytolytic agent carried into the egg-cell by the head 

 of the spermatozoon. TJie permeability of the surface of the cell is 

 also increased for inorganic salts, for McClendon has shown that the 

 Electrical Conductivity of a suspension of sea-urchin eggs is increased 

 by fertilization while Osterhout has shown that an increase in the 

 electrical conductivity of living tissues is indicative of increased per- 

 meability of the surface of the cell for inorganic salts. 



Since the lipoidal droplets in cells are suspended in a gelatinous or 



