SOAPS, PROTEIN DERIVATIVES AND TISSUES 233 



is no longer heat-coagulable. The analog for the behavior of 

 soaps of this type may be found in the basic derivatives of certain 

 globulins. 



We wish, finally, to touch upon some biological coagulations 

 in an attempt to define their nature more closely in the terms of 

 colloid-chemistry. Reference is made to the coagulations typical 

 of blood, milk and muscle juice. In all these instances a protein 

 body (fibrinogen, caseinogen, myosinogen) passes from a " sol- 

 uble " state to an " insoluble " clot (fibrin, casein, myosin). Be- 

 tween the two extremes, however, the originally liquid " plasma " 

 sets into a jelly which gradually develops signs of contracting with 

 the squeezing off of a " serum." The clot finally swims in this 

 serum as a relatively anhydrous mass. It is not our purpose to 

 enter into the debate concerning the chemical nature of the 

 various elements which are necessary for such coagulation. All 

 authors seem to agree that a substance x (" fibrin ferment," ren- 

 nin. muscle ferment) acts upon a second (fibrinogen, caseinogen, 

 myosinogen) to produce the clot, the production of the latter 

 being greatly favored by the presence of some of the earthy or 

 heavier metals such as calcium or iron. It would not yet " explain " 

 the physical changes accompanying the transformation of fibrino- 

 gen into fibrin even if it were proved (or disproved) that fibrin is 

 a true chemical union between calcium and fibrinogen. 



It will be apparent that the entire set of physical changes are such 

 as may be observed in the simple salting-out of a soap l and whatever 

 the ultimately accepted chemical fundaments of " clotting," the 

 physical transformation in the system must be of the same general 

 type as observed in the salting-out of a ,swi/j. It is necessary, in con- 

 sequence, to look at the soap system once more (see Fig. 74), to 

 grasp correctly the analogous changes in protein systems when 

 these " clot." 



The liquid " plasma " of Mood, milk or muscle juice is analogous 

 to a liquid colloid system, of the type sodium oleate/water. The 

 substance x (fibrin ferment, rennin, muscle ferment) which will 

 bring about clotting may l>e anything which will lead to the sej>- 

 aration of a second plia<e within the hydrated sodium oleate. 

 It must in consequence be either (1) a substance which, like sodium 



1 See page li:t 



