Effect of Salts and Adds on Biocolloids and Cell-masses. 45 



expansion in acids, the action of the solution being supplemented by 

 the amino-acid in the sections, in a manner similar to that of such other 

 amino-acids as aspartic acid, cystin, tyrosin, etc. 



A mixture of agar (50 parts) and gelatine (50 parts) poured on 

 Pratt-Dumas brown filter-paper dried to a total thickness of 0.3 mm. 

 Swellings of this were made in the dark chamber at a temperature of 

 16° C, with the results shown in table 33. 



Tabue 33. 



p. ct. 



Distilled water 400 



Potassium nitrate 375 



Potassium nitrate, citric acid, 0.01 M 350 



Citric acid, 0.01 N 300 



Potassimu hydrate, potassium nitrate, 0.01 M 425 



Potassium hydroxid, 0.01 M 325 



These results, so far as they may be correlated with the earlier ones, 

 show an unexpected relation to acid, hydroxid, and water. It is to be 

 noted in addition, however, that a combination of potassium hydrate 

 and potassium nitrate gives the maximum effect in the series. 



The apphcation of parallel tests to growing tissues is complicated 

 by the fact that varying quantities of normal salts and acid salts may 

 be present, giving a buffer effect. The concentration of the hydrogen 

 ion may be determinable by estimation of the titrable acid and the 

 dissociated malates, for example, as found by Jenny Hempel, but in 

 addition there are to be considered the effects of the amino-acids and 

 amines, which are not easily to be measured. 



Leaves of Mesembryanthemum edule, which were not yet fully grown, 

 were cut into sections about a centimeter long and allowed to dry 

 in the air. When the greater part of the water had been lost and the 

 sections had a leathery consistency, one of the angles was removed 

 with the scissors, leaving a specimen 1.8 mm. thick. The preparations 

 were by no means uniform. The use of three to obtain each record 

 would tend to obviate or smooth the discrepancies, but the data given 

 in table 34 can not be taken as having been obtained from preparations 

 strictly equivalent. 



Table 34. — Swelling of sections of Mesembryanthemitm. 



p. ct. 



DistiUed water 72 



Potassium nitrate, 0.01 M 69 



Potassium nitrate, 0.1 M 66 



Citric acid, potassium nitrate, 0.01 M 44 



Citric acid, 0.01 N .' .' 72 



Sodium hydroxid, 0.01 M 28 



The main interest in this set of reactions is that directed to the 

 comparison of the swellings in potassium nitrate, citric acid, and the 

 combination at the same concentration. The coefficient of swelling 

 in the plant-like sections of agar-oat protein and agar-bean protein was 

 least in the acidified salt solution, although the hydrogen-ion concen- 



