224 



SCIENCE 



[N. S. Vol. XLII. No. 1076 



colloids (as when gelatin " dissolves " under 

 the influence of a rise in temperature) may 

 be, and have been called upon to explain the 

 origin of the albumin appearing in the urine 

 in certain types of kidney disease, in the li- 

 quids which are squeezed off by heavily hy- 

 drated (edematous) tissues (the so-called 

 "transudates"), etc. 



On the basis of such concepts, excessive 

 turgor, plasmolysis and edema may be deiined 

 as states of increased hydration of the (hy- 

 drophilic) body colloids, while albuminuria 

 (when not simply due to gross rupture of 

 blood and lymph vessels with escape of their 

 contents) may be defined as a state of in- 

 creased " solubility " of the kidney colloids. 

 The causes of an edema or of an albuminuria 

 are, in their turn, to be found in the condition 

 or conditions which are capable of bringing 

 about these physicochemical changes in the 

 colloids of the body. As of dominant impor- 

 tance in this matter I have emphasized the ab- 

 normal production or accumulation of acid in 

 the pathologically involved tissues, though as 

 I have pointed out many times before, this 

 need not be, and probably is not, the only 

 cause for the observed colloid-chemical changes. 



The almost constant association of edema 

 with a "solution" of the body proteins (as, 

 for example, a swelling of the kidney with an 

 albuminuria) suggested from the first that 

 the same cause might lie behind both. In 

 order to prove that this is the case, I have not 

 only described acid intoxication experiments 

 on animals which result constantly in the pro- 

 duction of an edema of the kidney (and other 

 organs) and an albuminuria, but also obser- 

 vations on pure proteins (fibrin, gelatin, etc.) 

 which show that the same acid which leads to 

 the increased swelling also leads to " solu- 

 tion " of the proteins. 



It is a commonly accepted view that the 

 " solution " of a protein represents but the ex- 

 treme of that which in lesser degree is called 

 swelling. So far as I know, it has been held 

 almost universally that sufficient hydration, 

 results as a matter of course, in " solution." A 



warning against the general adoption of this 

 view has been sounded before.^ 



I have recently been working on gelatins at 

 concentrations and at temperatures near their 

 gelatin and melting-points. Working in this 

 region has yielded results which prove con- 

 clusively that the phenomena of hydration 

 (swelling) and of " solution " in protein gels, 

 while frequently associated, are essentially 

 different. Hydration is to he regarded as a 

 change through which the protein enters into 

 physicochemical comhination with its solvent 

 {water) ; " solution," as one which can he most 

 easily understood at the present time as the 

 expression of an increase in the degree of dis- 

 persion of the colloid. The experiments show 

 that the increase in degree of dispersion is, 

 on the whole, antagonistic to the hydration 

 process, in that more finely dispersed colloid 

 particles seem incapable of holding as much 

 water as coarser ones. 



For the experiments I used a commercial 

 gelatin very low in salts which previous ex- 

 periments had shown to be capable of great 

 swelling with maintenance of form. Even so 

 dilute a mixture as an 0.8 to 0.9 per cent, so- 

 lution of the stock gelatin would set into a 

 solid mass when left to itself for a few hours 

 at 25° C. The experiments were carried out 

 with 2 per cent, gelatin. This formed a very 

 stiff gel upon which the eflfects of different 

 added substances were then studied. The con- 

 clusions from such studies may be summed up 

 as follows : 



1. The addition of acids and alkalies to 

 gelatin markedly decreases its tendency to gel. 



2. The addition of acid or alkali will not 

 only prevent gelation of a liquid gelatin but 

 it will at the same concentration make a 

 solid gelatin liquefy. 



3. The addition of proper amounts of vari- 

 ous salts to acid- or alkali-gelatins which in 

 themselves would never gel leads to their 

 prompt gelation, in other words, the salts an- 

 tagonize the liquefying action of the acid or 

 alkali. 



4. The salts show an optimum in their in- 

 ^ See Martin H. Fischer, ' ' CEdema and Ne- 

 phritis, ' ' second edition, 433, 444, New York 

 (1915). 



