August 13, 1915] 



SCIENCE 



225 



hibitive effects upon, tlie liquefying influence 

 of acids and alkalies. 



5. At the same concentration different salts 

 are unequally effective in their power of pro- 

 ducing gelation in liquid acid- or alkali-gela- 

 tins. Speaking generally, trivalent radicals 

 are more active in this regard than bivalent 

 ones, and these than univalent ones. 



6. A quantitative relationship exists be- 

 tween the liquefying power of an added acid 

 and the antagonistic action upon this of a 

 salt. Gelatin mixtures containing a definite 

 concentration of some salt, and solid when a 

 certain concentration of an acid is established 

 in them, begin to soften and finally to liquefy 

 as the acid concentration is raised. 



7. Other substances besides acids and alka- 

 lies favor the liquefaction of gelatin. Urea, 

 pyridin, and the amins are found in this group. 



m 

 These experiments have a bearing upon 

 certain problems in colloid-chemistry and in 

 biology and medicine. Under the former head- 

 ing they bring the first proof, as far as I know, 

 that hydration and solution in proteins is not 

 the same thing. We seem to be justified in the 

 assumption that gelatin is a chemical sub- 

 stance capable of existing in different degrees 

 of association or polymerization. Depending 

 upon the temperature and other changes in its 

 environment, the degree of this association, 

 and hence the size of the particles of which 

 the gelatin is composed, may be greatly varied. 

 At higher temperatures, under the influence 

 of acids and alkalies, etc., the particles become 

 small, while under the reverse conditions they 

 become larger. With these changes in size 

 they change their physicochemical properties 

 so that under the former circumstances they 

 are liquid and clear, while under the latter 

 they become solid and opalescent. The par- 

 ticles seem capable of absorbing most water 

 (becoming most heavily hydrated) when they 

 have a medium diameter. Entirely neutral 

 gelatin (in which the particles are large) 

 therefore absorbs some water, which on the 

 addition of acid (which multiplies the par- 

 ticles and makes them smaller) is increased. 

 On further addition of acid, however, the par- 



ticles decrease in size to beyond that optimal 

 for swelling. In this region the mixture, as a 

 whole, begins to liquefy and shortly there- 

 after begins to show prominent evidences of 

 going into " solution." 



In " swelling " experiments this region cor- 

 responds with that where with progressive in- 

 creases in the concentration of acid the stead- 

 ily mounting curve of water absorption begins 

 to fall. It really means that the division of 

 the gelatin particles has progressed beyond 

 the point at which they hold their greatest 

 amount of water. 



The addition of salts to gelatin increases 

 the size of the particles and in so doing brings 

 them back toward the region more nearly 

 optimal for hydration. As the salt makes the 

 gelatin stiffer its opalescence again increases.^ 



From a biological point of view these ex- 

 periments bring renewed evidence of the pro- 

 tein nature of the reactions in living cells in 

 which an antagonism is observed between acids 

 (or alkalies) and neutral salts. They also 

 show why with a gradually mounting degree 

 of acid intoxication in living matter, more 

 and more salt is necessary to keep the affected 

 proteins in a given physical state; in other 

 words, why in clinical medicine more than 

 " physiological " salt solutions, namely, so- 

 called " hypertonic " ones, must be used in 

 order to reduce an edema, an albuminuria, or 

 similar states. Why salts with bivalent or 

 polyvalent radicals have so long been recog- 

 nized as of special aid in these practical clin- 

 ical problems is also evident from these ex- 

 periments. 



The experiments also explain why injured 

 tissues pass, as a rule, through a primary 

 period of swelling into a second one of soften- 

 ing. Under the influence of the acids (and 

 similarly acting substances) brought into play 

 by the injurious agents the tissues first swell, 

 but as the acid content rises protein dissocia- 



3 As will be shown in another communication, 

 most of these statements hold for other proteins 

 also. It is well to emphasize even here, however, 

 that the salts tend to increase the size of the par- 

 ticles and thus dominantly to favor hydration 

 under certain circumstances only in gelatin. 



