SYNERESIS 401 



either acids or alkalis. In the case of fibrin M. H. Fischer * 

 was able to increase the normal swelling in water sixfold by 

 the presence of 0-02 N hydrochloric acid. As a practical ap- 

 plication of this may be mentioned the beneficial effect of the 

 addition of a small quantity of acetic acid to the water em- 

 ployed for swelling agar previous to making a solution. 



With regard to the action of salts, it is found that anions 

 act in the order of the Lyotropic series mentioned on page 



398. 



Thus the following anions favour imbibition : — • 



CNS > I > Br > NO3 > CIO2 > CI ; 



while the following inhibit — 



— SO4 >• tartrate >• citrate >■ acetate, 



as do also alcohol, glucose, and cane sugar. 



According to Spek f salts such as lithium bromide or 

 potassium thiocyanate, which have a strong influence on the 

 swelling of colloids, also accelerate the rate of cell division 

 of Paramoecium, while calcium chloride and sulphates, which 

 reduce swelling, retard cell division. 



Many of the epidermal tissues in plants and animals 

 are cuticularized or otherwise hardened ; this prevents their 

 swelling when brought in contact with water, thus enabling 

 them to maintain their shape, and it is a commonplace in 

 histological technique to harden tissues by immersion in 

 formaldehyde or other solutions so as to counteract and pre- 

 vent this same tendency. The hardening of gelatine by 

 means of bichromate is another example of the same principle. 



Syneresis. — This is the name given by Graham to a 

 phenomenon which may be regarded as the reverse of swelling. 

 Most gels, on keeping, squeeze out a small quantity of liquid 

 which is not pure water but a dilute solution of the colloid in 

 question. The amount of liquid thus exuded varies with 

 the concentration of the gel, and is greater for some colloids 



* This author considers that much of the pathological swelling in 

 animals and man is due to an accumulation of acid in the tissues, which, as 

 a consequence, tend to draw fluid from surrounding tissues and so swell ; 

 he would even offer the same explanation for the swelling caused by an 

 insect's bite. 



t Spek : " KoU. Chem. Beihefte.," 1920, 12, i. 



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