114 



Hydration and Growth. 



have detected a very small expansion, while satisfaction was nearly 

 complete in 8 hours at 46 to 47 C. 



We may now profitably turn to an extension of the reactions of the 

 salted colloids (seep. 111). Sections of agar, bean protein, and nutrient 

 salts 0.18 mm. in thickness gave the expansions shown in table 91 at 

 31 C. 



The temperature series was taken another step by raising the air 

 in the chamber to 42 C., at which point the liquid in the dishes showed 

 38 to 39 C., being cooled by evaporation to this point. The measure- 

 ments are given in table 92. 



TABLE 92. 



The increase of the temperature of the air in the chamber to 52 C. 

 gave a temperature of 46 to 47 C. to water in the dishes. The swell- 

 ings at 46 to 47 C. are shown in table 93. 



TABLE 93. 



A review of the action of the salted mixture shows a very slight 

 acceleration by the rise in temperature from 22 C. to 31 C. and also 

 a total but slightly increased above that of the lower temperature. 

 The next step, from 31 to 39 C., however, was one marked by a 

 distinct acceleration, the rates during the first 4 hours being as 15 to 

 25, during the first 8 hours as 17 to 27, and the final total at the lower 

 temperature at 20 hours was as 20 to 28 at the higher temperature at 

 the end of 12 hours. 



The absorption of water fell off at temperatures above 39 C., which 

 may be regarded as in the region of the optimum or maximum water- 

 holding capacity, which is somewhat lower than that of the salt-free 

 mixture. Many repetitions of the tests would be necessary before the 

 matter of the failure to show expected increase of hydration between 

 23 and 31 C. was accepted as a reality. The measurements in ques- 



