SWELLING OF PROTEIN JELLIES 307 



of the protein salt leads to an increase in the number of colloidal par- 

 ticles per unit volume of the jelly, and possibly, also,, in part, to the 

 fact that protein ions have a greater affinity for water than undisso- 

 ciated protein molecules. 



This conception of the process of swelling would still yield no equi- 

 librium or Swelling-maximum were there no compensating force acting 

 in an opposite sense to the osmotic pressure of the gelatin itself. No 

 matter how much gelatin may be diluted by swelling, there will always 

 remain an excess of osmotic pressure within the jelly, due to the protein 

 ions which cannot leave it. Now gelatin plates, when immersed in 

 water or in acid solutions, do not swell indefinitely until swelling 

 merges insensibly into solution, but, on the contrary, display a definite 

 swelling-maximum. At this point, therefore, the osmotic pressure 

 exerted by the colloidal particles within the jelly must be balanced by 

 an equal opposing force, which Procter interprets as the tension of 

 the elastic colloidal network. 



The effects of Inorganic Salts upon the swelling of gelatin plates are 

 complex because, as Loeb has recently demonstrated, they consist of 

 two separate factors: In the first place a chemical interaction occurs 

 between the gelatin and the salt, leading to the formation of a compound 

 of the acid component of the salt with the gelatin. This compound 

 has a greater swelling-capacity than uncombined gelatin. On the 

 other hand the uncombined portion of the salt, when present in excess, 

 tends in varying degree, depending upon the particular salt employed, 

 to dehydrate the gelatin and therefore to inhibit swelling. The power 

 of the various salts to inhibit the swelling of gelatin is proportionate 

 to their power of coagulating proteins in solution. 



The swelling of Living Tissues when immersed in hypotonic solutions 

 or in acid or alkaline isotonic solutions is a very complex phenomenon . 

 In the first place it is determined by the Permeability of the surfaces 

 of the cells for water and anything affecting the permeability of the 

 cells of the tissue will also influence the imbibition of water. In the 

 second place the swelling of the tissue is determined by the Osmotic 

 Pressure of the proteins which it contains, which is affected by acids, 

 alkalies and salts in the manner outlined above for gelatin. In the 

 third place degenerative changes in excised tissues such as the excised 

 muscles of the frog's leg, lead sooner or later to production of diffusible 

 products of Autolysis, and since the surface-layers of the tissue are 

 with difficulty penetrable by some of these, their production leads to a 

 greatly enhanced imbibition of water. 



Finally, the water which is taken up by the tissue may actually 

 enter the cells or, on the contrary, may merely be taken up into the 

 interstitial spaces between the cells. In general it may be stated, 

 however, that any factor tending to injure the vitality of the cells, 

 for example heating, will greatly increase their permeability for water, 

 and hence will increase the rate and degree of swelling in hypotonic 

 solutions. 



