24 Hydration and Growth. 



Other substances were next tested which are insoluble in water and 

 hence might not be expected to enter into the two-phase system with 

 agar. Mr. E. R. Long prepared some zein, a protmaine derived from 

 Zea mais, at his laboratory at Seattle, Washington, early in July 1917, 

 and this was made up with 1 part of zein to 9 of agar. 



The fine, iregular particles, after being wetted, were stirred into the 

 melted agar and the mixture was poured onto a glass slab and dried 

 down to a thickness of about 0.3 mm. The plate was rough to the 

 touch, the granular particles of the zein being distinctly visible as 

 opaque masses. Sections tested under the auxograph gave the meas- 

 urements as follows: 



TABLE 5. 



p. ct. 



Water 1,033.3 



Citric acid, 0.01 N 400 



Sodium hydroxid, 0.01 M 350 



The presence of the zein could not be said to be entirely without 

 effect, as these measurements show some departure from agar in the 

 relatively high swelling in acid. The imbibition in the hydroxid solu- 

 tion was extremely slow. Saturation was reached in 24 to 30 hours in 

 water and acid, but enlargement continued for twice this period in 

 hydroxid. All liquids were renewed at 36 hours. An acceleration ensued 

 in hydroxid and the swelling was still in progress at the end of 48 hours, 

 at which time the measurements were as above. Some of the equaliza- 

 tion or increase in the swelling of the biocolloid in acid and its con- 

 tinued swelling in hydroxid is probably due to the fact that zein is 

 slightly soluble in both acids and alkalies. 



The addition of I part globulin from beans to 9 parts agar resulted 

 in the formation of dried plates much like those of agar-zein. The 

 globulin, not being soluble in water, was incorporated as small globular 

 masses. Swellings of sections 0.2 mm. in thickness were exhibited as 

 shown in table 6, at 16 C. 







TABLE 6. 



p. ct. 



Distilled water 875 



Potassium nitrate, 0.01M 575 



Potassium nitrate, citric acid, 0.01 N 550 



Citric acid, 0.01 N 525 



Potassium nitrate, potassium hydroxid, 0.01 M 450 



Potassium hydroxid, 0.01 M 300 



The proportionate imbibition in water, acid, and hydroxid is one 

 characteristic of agar with a small proportion of protein. The solubility 

 of globulin in salt solutions would lead to the expectancy that its presence 

 would result in a modification of the swelling of agar in saline solutions. 1 



The " bean-protein " which has been used so extensively in these 

 experiments is, as noted elsewhere, an extract with water in which the 



1 See Zsigmondy, Behavior of globulins, in chemistry of colloids, p. 222. 1917. 

 Robertson, T. B. The physical chemistry of proteins. 1918. New York. 



