Effect of Salts and Adds on Biocolloids and Cell-masses. 43 



of gelatine and of the proteins and their derivatives will depend chiefly 

 upoii the proportions of such substances in the living cell-masses. The 

 properties of gelatine may illustrate those of protoplasm only in so far 

 as they are general to the elastic gels, in which class of colloids both may 

 be included.^ 



The salt-content of colloids of living matter in all probabiUty changes 

 very slowly, while the acidity may vary with great rapidity and through 

 a wide range. A set of tests were therefore arranged in which the 

 salt-content would remain constant while the solutions contained a 

 series of acid concentrations. The first series was one in which the 

 salt was dissolved in the solution of the acid after the manner in which 

 many measurements have been previously made. Sections of plates 

 of agar 90 parts and oat protein 10 parts which had an average thick- 

 ness of 0.18 mm. were cut so that a trio had a total volume when air- 

 dry of 12 cu. mm. and the dishes in which these were placed held about 

 30 c. c. of the solution. These measurements were made with the solu- 

 tions standing at 16° to 17° C. The results were as follows: 



Table 28. 



p. ct. 



Distilled water 1,722 



Potaasium nitrate, 0.01 M 1,250 



Potassium nitrate, 0.01 M + citric acid, 0.05 N 472 



Potassium nitrate, 0.01 M -j- citric acid, 0.01 N 528 



Potassium nitrate, 0.01 M + citric acid, 0.005 N 667 



Potassium nitrate, 0.01 M + citric acid, 0.001 N. 944 



Potassium nitrate, 0.01 M + citric acid, 0.0002 N 1,055 



Potassium nitrate, 0.01 M + citric acid, 0.00004 N 1,139 



The above measurements were taken at the end of 24 hours, at 

 which time the sections in distilled water and in the two solutions 

 containing least acid were still slowly expanding, at a rate which 

 would not have changed the final aspect of the test. These results 

 are of importance, since it has been found that the range of 

 acidity in such plants as growing joints of cacti may be practically 

 equivalent to that from the highest acid-content to the lowest during 

 the dayUght period, coincident with an enormous variation in the 

 water-capacity of the organ.^ The measurements of plates composed 

 of 90 parts agar and 10 parts bean protein 0.25 nun. in thickness, in 

 dark room, at 16° to 17° C, gave the results shown in table 29. 



Table 29. 



p. ct. 



Distilled water 1,280 



Potassium nitrate 1,060 



Potassium nitrate, citric acid, 0.01 M 802 



Citric acid, 0.01 N 604 



Potassiimi hydroxid, 0.01 M 604 



Effects similar to the original are to be discerned in the above. The 

 combination of acid and salt reduces the hydration capacity of the 



' Fenn, W. O. Similarity in the behavior of protoplasm and gelatine. Proc. Nat. Acad. Sci., 

 2: 539. 1916. 



' MacDougal, D. T., and H. A. Spoehr. The effects of acids and salts on biocolloids. Science, 

 46:269. 1917. 



