58 CARNEGIE INSTITUTION OF WASHINGTON. 



lism of a predominantly proteinaceous unit includes the derivation of 

 amino-aeids by breaking down albumins, while the amino-compounds 

 may be synthetized in the plant in which the amination of the car- 

 bohydrates is the theoretical step in the construction of nitrogenous 

 material. 



The main components of living matter are not soluble or diffusible 

 in each other, and they are therefore in an intimate non-homogeneous 

 mixture in a colloidal condition in which the separate particles are so 

 small as to give play to surface forces of great intensity. 



Growth, as has been defined, consists of two processes. First, the 

 molecules or aggregates of molecules of the two kinds, the carbo- 

 hydrates and the albumins, combine with and absorb water, thus 

 increasing the volume of these units, regardless of whether such par- 

 ticles be in the form of droplets or fibrillse of a mesh-work. Instances 

 of growth are known in which water only has been added to the colloidal 

 structure in which in all probability the solid particles have been 

 variously rearranged. In general, however, growth is accompanied 

 by the accretion of molecules of solid material in such manner that as 

 development proceeds their proportion to that of the water taken up 

 increases, and organs are then said to show an increase of relative dry 

 weight with age. 



On the other hand, my own studies have shown that succulent 

 organs or stems, such as leaves of the Crassulacese, joints of cacti, 

 fruits, etc., do not show such increase, and the proportion of solid 

 matter and of water undergo but little change, their incorporation 

 being at a rate which keeps them near the initial proportion. It is 

 suggested that such action may be shown by the fleshy fungi, although 

 I have not seen any data bearing directly upon this matter. 



The conditions under which hydration may ensue are by no means 

 identical for the two main constituents of living matter. Thus, the 

 albumins and their derivatives, as exemplified by the behavior of 

 gelatine, show a swelling determined or facihtated by the hydrogen-ion 

 concentration or acidity of the solutions, being increased as this rises. 

 The pentosans, on the other hand, show no such increase, and, being 

 weak acids, their hydration is retarded by the hydrogen ion. The 

 swelling of a mixture of the two ^vill therefore be a resultant of these 

 effects and of the proportion of the two elements in the living mixture, 

 and as the unceasing action of respiratory metabolism results in the 

 formation of some residues of acids, the condition of hydration of any 

 mass of protoplasm may be said to reach a volume determined by 

 these opposed reactions. The fundamental properties of a colloidal 

 mixture or of living matter will depend upon the proportion of albumins 

 and of pentosans, and upon the properties of the particular substances 

 of each group which may be present. Hydrogen ions within the pos- 

 sible range of concentration increase hydration of the albuminous 



