CONDITION OF AGGREGATION OF ORGANISED STRUCTURES. 667 
organised body, so that they act upon and decompose one another. It is certain 
that all growth continues only so long as the growing parts of the cell are exposed 
to atmospheric air ; the oxygen of the air has an oxidising effect on the chemical 
compounds contained in the organised structure ; with every act of grow th carbon 
dioxide is produced and evolved. The equilibrium of the chemical forces is also 
continually disturbed by the necessary production of heat; and this may also be 
accompanied by electrical action. The movements of the atoms and molecules 
within a growing organised body represent a definite amount of work, and the equi- 
valent forces are set free by chemical changes. The essence of organisation and 
of life lies in this : — that organised structures are capable of a constant internal 
change ; and that, as long as they are in contact with water and with oxygenated 
air, only a portion of their forces remains in equilibrium even in their interior, and 
determines the form or framework of the whole ; while new forces are constantly 
being set free by chemical changes between and in the molecules, which forces in 
their turn o.ccasion further changes. This depends essentially on the peculiarity of 
micellar structure, which permits dissolved and gaseous (absorbed) substances to 
penetrate from without into every point of the interior, and to be again conveyed 
outwards. 
This internal instability attains its highest degree in chlorophyll-granules and pro- 
toplasm. In the former chemical processes take place with great energy and activity 
under the influence of light, such as the formation of the green colouring matter and 
of starch ; and when deprived of light other chemical changes at once ensue, which 
terminate only with the complete destruction of the entire chlorophyll-granule. The 
remarkable properties of protoplasm, which we have already examined from different 
sides in discussing the structure of the cell, attain their climax in its spontaneous 
automatic power of motion, and in its capacity of assuming different forms and 
changing both its shape and its internal state, and therefore of bringing into action 
internal forces, even when corresponding impulses from without cannot be observed. 
It is impossible to enter here in detail into the explanation of these remarkable facts; 
but they will be understood, at least generally and to a certain extent, if it is borne 
in mind that neither the chemical nor the molecular forces are ever in equilibrium in 
the protoplasm ; that the most various elementary substances are present in it in the 
most various combinations ; that fresh impulses to the disturbance of the internal 
equilibrium are constantly being given by the chemical action of the oxygen of the 
air ; and that energy is continually being set free at the expense of the substance of 
the protoplasm itself, which must lead to the most complex actions in a substance of 
so complicated a structure. Every impulse from without, even when imperceptible, 
must call forth a complicated play of internal movements, of which we are able to 
perceive only the ultimate effect in an external change of form. 
The destruction of the micellar structure of organised bodies may take place in 
many different ways, and affords an insight into many physiological processes. 
The most important forces by which the micellar condition of organic substances 
is permanently altered are changes in temperature, chemical reagents, and substances 
which have a powerful attraction for water. But these agencies do not in general 
cause destruction until they have exceeded a definite degree of intensity ; while dif- 
ferent changes of temperature and different states of concentration of the reagents 
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