MECHANISM OF PROTEIN HYDROLYSIS AND IMMUNIZATION 57 



burn their other constituents; whereas the protein molecule, in 

 order that it may not be too unstable, is provided with a com- 

 paratively small supply of oxygen. 



Recall now the principles of osmosis, as revealed by the studies 

 of Van't HofT. It appears that osmosis, or the passage of liquid 

 through a membrane from one solution to another, is due, not 

 to any suction principle, but to the pressure on the membrane 

 exerted by the molecules of the denser liquid; that is to say, the 

 liquid which has the larger number of free molecules in a given 

 volume. 



A single liberated atom or ion of oxygen or any other element 

 is the osmotic equivalent of the most gigantic protein molecule. 



This is the curious fact discovered by Van't Hoff, and substan- 

 tiated through the researches of Arrhenius and Ostwald. It is 

 of fundamental importance in its application to the relations of 

 the living cell. 



Suppose, for example, that a full-sized protein molecule in the 

 protoplasm of a living cell were suddenly to be disrupted into 

 molecules of its component substances, the amino-acids. Imme- 

 diately the osmotic pressure exerted by the molecule would be 

 increased a hundred fold. The pressure might disrupt the cell- 

 Short of that, it would result in pressing the cell wall outward 

 against the surrounding fluid, with the result that a certain 

 amount of that fluid would pass through the cell wall and be- 

 come a part of the cell content. Suppose, then, just as equi- 

 librium of pressure between the cell and its surroundings is re- 

 established, there is a recombination of the dissociated elements 

 to produce full-sized protein molecules. A hundred or so amino- 

 acid molecules becoming a single protein molecule, the osmotic 

 pressure in the cell would be correspondingly reduced, with the 

 result that the cell would contract under stress of outside pres- 

 sure and exude a portion of its content. 



It is not unlikely that this process may explain the enigmatic 

 action even of such highly developed cells as the muscle cell in 

 the animal body, the contraction of which has never been clearly 

 understood. 



I am not unaware that some physicists have denied that the 

 laws of osmosis apply to colloidal substances. But, aside from 

 the apriori improbability that these liquids defy the operation of 

 so fundamental a law, the balance of evidence seems corrobora- 

 tive. And, as regards the particular application in hand, there 

 is, I believe, no alternative hypothesis that explains muscular 

 action so satisfactorily. A decompounded molecule of muscle- 

 cell protein becomes, let us say, one hundred molecule of amino- 

 acids; and the osmotic pressure within the cell is increased a 

 hundred fold. The swelling and hardening of the muscle, with 



