BOOK III. 
PHYSIOLOGY. 
CHAPTER L 
MOLECULAR FORCES IN THE PLANT. 
Sect. i. — The Condition of Aggregation of organised structures^. 
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stance capable of removing water, a part of their aqueous contents is withdrawn ; 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. — Nägeli u. Schwendener, 
Das Mikroscop, p. 422 et seq. ; compare also Book I of this work, p. 28 et seq. — Cramer, Naturforbch, 
Gesells. in Zürich, Nov. 8, 1869. 
^ Jungk, in Pogg. Ann. 1865, vol. 125. p. 292 et seq. 
