68 CARNEGIE INSTITUTION OF WASHINGTON. 



than in the control. This difference in growth rates raay be observable 

 in the earlier phase only in the case of potassium. 



It would seem that the potassium is absorbed more vigorously 

 than is sodium by the protoplasm or by some element in the colloidal 

 complex at present regarded as protoplasm. A toxic effect also is more 

 obvious in the case of potassium. The observations have bearing on 

 the comparative physiological effects of these two metals. 



Temperature and the Hydration and Growth of Colloids and of Cell-Masses, 



by D. T. MacDougal 



Recognition of the complex character of the groups of reactions 

 which enter into the more prominent life-processes has brought 

 conviction as to the futility of attempts to define physical constants, 

 such as temperature coefficients. For example, variation in tempera- 

 ture results in modification of the rate of enzymotic processes and of 

 the forms of metabolism included under and associated with respira- 

 tion; modification of the rate of absorption of water by the organisms 

 from its medium or substratum; modification of the water-holding 

 capacity of the cell-colloids after a mode determined by their carbo- 

 hydrate protein ratio and by the state of acidosis. The actual increase 

 in volume will also be influenced to some extent by the water-loss 

 which takes place. 



A determination of the effect which temperature might have on 

 growth necessarily takes into account first the fundamental increase 

 which might accrue from simple absorption under various conditions. 

 In recognition of this fact, it was arranged to carry on swelhngs of 

 some of the biocoUoids in order to gain some appreciation of the 

 imbibition factor in growth. Sections (2 mm. in thickness) of plates 

 of agar and of agar 90, bean protein 10, and nutrient salts 0.85 per 

 cent, were swelled at temperatures of 15° C. to 49° C. in a constant- 

 temperature room. The differentiated effects are illustrated by the 

 following set of measurements : 



The hydration reactions of the agar are not so positive and uniform 

 as those of the biocoUoids. Increase by absorption had not reached a 

 positive final in 24 hours at the lowest temperature. A similar stage 

 of satisfaction was evident in half this time at about 40° C. and in 

 8 hours at 49° C. The maximum or "optimum" of swelling of such 

 agar plates occurs at some temperature near 40° C. Initial rate and 

 total increase are greatest at this point. 



The agar-oat protein mixture has a higher maximum initial capacity 

 at 46° to 47° C, but does not appear to absorb as much water as at a 

 temperature a few degrees lower. The maximum swelling of the 

 agar-bean protein and salt mixture lies below 46° C. and is probably 



