112 



Hydration and Growth. 



hour of immersion, with consequent great rapidity of swelUng. It is 

 not possible to separate this action from adsorption, which follows more 

 slowly, but if the first 4-hour period be considered, it is to be seen that 

 the total rises from about 9 to 14, with a change from 15° to 22° C. at 

 which the immersion was made. If the first 8 hours is considered, the 

 hydration as expressed by the total swelling is as 11 to 16 at the two 

 temperatures and as 13 to 19 for the entire period of hydration, a ratio 

 which includes the accelerating effects of a rise in temperature both on 

 the initial chemical action and the continued absorption.^ 



A biocoUoid without salts consisting of 9 parts agar and 1 part oat 

 protein was now tested for comparison, with results shown in table 87. 



Table 87. 



The swelling during the initial period of this salt-free mixture is 

 actually greater than that of the first mixture, but is affected in far 

 less degree by the rise in temperature, the ratio at 15° C. and at 23° C. 

 being as 12 to 13. The difference, if the 8-hour period is considered, 



8 p.m. 



Fig. 20. — Tracing of autographic records of swelling of plates 0.18 mm. in thickness, consisting 

 of 9 parts agar and 1 part oat protein, a "biocoUold" with very high hydration capacity. 

 The 5 mm. and 4-hour intervals of the record sheet are shown. Increase is denoted by the 

 downward movement of the pen, which amplifies the actual swelling 20' times. The variap 

 tion in initial and following rates and time necessary for hydration are shown. 



was as 16 to 10, and for the 23-hour period, as 18 to 25. It is suggested 

 that the chemical action during the beginning stages of swelling is far 

 less important than in the salted mixture and that the entire set of 

 reactions is one in which absorption and hydrolysis play the determin- 



^ MacDougal. The relation of growth and swelling of plants and biocolloids to temperature. 

 Proc. Soc. Esper. Biol, and Med., 15:48. 1917. 



