286 



Miss D. J. Lloyd. 



The Relation of Gelatine to Acids, Salts, and Bases. 



The curve of maximum swelling of excised muscle in acid or alkaline 

 media is the curve of swelling of some substance in the colloidal state. A 

 search through the literature of colloidal chemistry reveals almost as 

 complete a paucity of systematic data as was found in the more physiological 

 domain of muscular phenomena. Wo. Ostwald(15) has published curves for 

 the swelling of gelatine in acid and alkali. These curves agree with the 

 curves for muscle in showing increased swelling of gelatine with increased 

 concentration of acid and alkali up to a maximum, and afterwards decreased 

 swelling. Ostwald's curves differ from the muscle curves in three important 

 points : firstly, the maxima for both acid and alkali are at a concentration of 

 about - 02o normal ; secondly, the downward slope of the curves beyond 

 these points is very gradual, and finally there is a minimal swelling for acid 

 at 0"005 normal. 



The relation of gelatine to acids and salts has also been studied by 

 Proctor (17 and 18). His curve for the swelling of gelatine in dilute 

 hydrochloric acid corresponds remarkably closely with the curve for muscle. 

 The maximum for both curves is in the neighbourhood of O'OOo normal acid, 

 and the curves again rise very steeply to this maximum and slope away 

 sharply beyond it. Proctor explains the swelling of the gelatine on the 

 assumption of the formation of an ionisable salt of the weak diacidic base, 

 gelatine. He finds that this assumption not only explains the fixation of the 

 hydrogen and chlorine ions by the gelatine, but also explains the swelling of 

 the gelatine on a simple osmotic basis. If his theory is valid for gelatine, 

 it must, from the similarity of the two curves, also be valid for muscle, and 

 it leads to the assumption that in a muscle immersed in acid solution, there 

 is chemical interaction between the muscle colloids and the acid, leading to 

 the formation of ionisable salts, which, exerting a definite osmotic pressure 

 against the elastic forces of the muscle, cause swelling. Proctor states that 

 the colloidal cation of his gelatine chloride does not contribute directly to 

 the osmotic pressure. This view, however, is not in harmony with much 

 work that has been done on the direct determination of the osmotic pressure 

 of gelatine gels, and I am not, at the moment, prepared to follow so far. 



Finally, Lillie (10) has made an extensive series of experiments by direct 

 measurement on the osmotic pressure of gelatine and egg albumen, and has 

 shown : — 



" (1) The osmotic pressure of colloids is unaffected after the addition of 

 non-electrolytes (sucrose, dextrose, glycerine, urea). 



" (2) Acid and alkali increase the osmotic pressure of gelatine solutions ; in 



