SOAPS, PROTEIN DERIVATIVES AND TISSUES 231 



For a few of the proteins (as gelatin) in the presence of the light 

 metal bases, the effects of temperature may be dismissed with the 

 statement that raising the temperature merely moves the system 

 in the direction of true solution in water. As ordinarily stated, 

 the proteins are " more soluble " at the higher temperatures and 

 are " not coagulable " by heat. The same might, of course, be 

 said of the " solubility " of the lower fatty acids when these, in 

 the presence of sodium or potassium hydroxid and water are raised 

 in temperature. When the same proteins are examined in the 

 presence of magnesium or calcium their behavior becomes "ambig- 

 uous," while in the the presence of heavy metals the proteins are 

 uniformly coagulable at all temperatures. The reasons for this 

 are to be found in the fact that many of the magnesium and 

 calcium proteinates (like the magnesium and calcium soaps) are 

 little more " soluble " at higher temperatures than at lower ones, 

 while all the heavy metal proteinates, like the heavy metal soaps, 

 have a low hydration capacity and a low solubility in water at all 

 temperatures. 



The accepted example of heat coagulation (or heat denaturfza- 

 tion of the " protein ") is, however, best seen in certain of the pro- 

 teins like various albumins and globulins. Here rise in temperature 

 even in the presence of light metals does not favor hydration and 

 solution of the " protein " but just the reverse. Where in the 

 colloid-chemistry of the soaps do we encounter an analogous set of 

 facts? Nowhere in the group of the systems composed of pure soaps 

 and little water, but in the behavior of those in which through hydroly- 

 sis or otherwise the separation of insoluble free fatty add is favored. 

 In the case of the" heat coagulable " proteins it is also a matter, not of 

 the coagulation of the potassium, sodium, etc., proteinates through 

 increase in temperature but of the free (proteinic) acid formed after 

 hydrolysis. The items which favor such heat coagulation are the 

 items which make for increase in hydrolysis or displacement of the 

 system in the direction of a higher concentration of free proteinic 

 acid. The heat itself does this, though the whole process is 

 favored by dilution of the system with water, and the addition 

 of small amounts of acid. Heat-coagulated protein/water systems 

 are considered as among the most typical of the irreversible 

 c (..i^ul.itions. Reversible, however, they are, as witness their 

 MS riling and solution when such " denatured " proteins are treated 

 with light metal hydroxids. The same phenomena are observable 



