BOOK III. 



PHYSIOLOGY. 



CHAPTER I. 

 MOLECULAR FORCES IN THE PLANT. 



Sect. i. — The Condition of Aggregation of organised structures i. 



Cell-walls, starch-grains, and protoplasmic structures consist, in their natural con- 

 dition, at every point that can be seen even under the microscope, of a combination 

 of solid material with water. If these organised structures are placed in a sub- 

 stance capable of removing water, a part of their aqueous contents is withdrawn ; 

 while, on the other hand, if they are in contact with aqueous solutions possessing 

 certain chemical properties and of a proper temperature, they absorb more water. 

 The volume alters with the change in the proportion of water ; loss of water causes 

 diminution, absorption of water a corresponding augmentation of volume. Since 

 the absorption of water occasions a considerable elevation of temperature (air-dry 

 starch rises 2° or 3° C. when mixed with water of the same temperature), it must 

 be supposed that the water becomes denser as it is absorbed^. ' Within certain limits 

 these variations in the proportion of water may occur without occasioning any per- 

 manent change in the intimate structure ; but if, with a higher temperature and in 

 the presence of chemical reagents, the proportion falls below a certain minimum 

 or exceeds a certain maximum, permanent changes of the intimate structure take 

 place which can no longer be reversed ; and the internal organisation of the body 

 becomes partially or entirely destroyed. 



' See Sachs, Handbuch der Experimental-Physiologie, p. 398 et seq. — Nageli u. Schwendener, 

 Das Mikroscop, p. 422 et seq. ; compare also Book I of this work, p. 28 et seq. — Cramer, Naturforsch. 

 Gesells. in Ziirich, Nov. 8, 1869. 



2 Jungk, in Pogg. Ann. 1865, vol. 125. p. 292 et seq. 



