THE BEGINNINGS OF LIFE. 89 



says 1 : c Among the latter are hydrated silicic acid, 

 hydrated alumina, and other metallic peroxides of the 

 aluminous class, when they exist in the soluble form j 

 with starch, dextrine and the gums, caramel, taurin, 

 albumen, gelatine, vegetable and animal extractive 

 matter. Low diffusibility is not the only property 

 which the bodies last enumerated possess in common. 

 They are distinguished by the gelatinous character of 

 their hydrates. Although often largely soluble in water, 

 they are held in solution by a most feeble force. They 

 appear singularly inert in the character of acids and 

 bases, and in all the ordinary chemical relations. But, 

 on the other hand, their peculiar physical aggregation, 

 with the chemical indifference referred to, appears to 

 be required in substances that can intervene in the 

 organic processes of life. The plastic elements of the 

 animal body are found in this class.' These compounds 

 are so all-important in living organisms, both from 

 a structural and from a functional point of view, that 

 it is most desirable to learn as much as we can con- 

 cerning their properties as mere material aggregates 

 i. e. when they exist alone and not as constituents 

 of living bodies. We find that they themselves exhibit 

 a constant tendency to change in response to the most 

 delicate impressions, after a fashion which is suggestive, 

 at least, of the more complex though still comparatively 

 simple action and interaction taking place between one 

 of the lowest kinds of Amoebae and its environment. 



1 'Phil. Trans.' 1861, p. 183, 



