SIMPLE AND COMPOUND EVOLUTION. 309 



And since many equivalents of these gaseous elements unite 

 in one of these protein-molecules, there must be in it a large 

 quantity of relative motion in addition to that which the 

 ultimate atoms possess. Moreover, organic matter 



has the peculiarity that its molecules are aggregated into 

 the colloid and not into the crystalloid arrangement; form- 

 ing, as is supposed, clusters of clusters which have 

 movements in relation to one another. Here, then, 

 is a further mode in which molecular motion is in- 

 cluded. Yet again, these compounds of which 

 the essential parts of organisms are built, are nitrogenous; 

 and we have lately seen it to be a peculiarity of nitrogenous 

 compounds, that instead of giving out heat during their 

 formation they absorb heat. To all the molecular mo- 

 tion possessed by gaseous nitrogen, is added more 

 motion; and the whole is concentrated in solid pro- 

 tein. Organic aggregates are very generally dis- 

 tinguished, too, by having much insensible motion in a 

 free state the motion we call heat. Though in many cases 

 the quantity of this contained insensible motion is incon- 

 siderable, in other cases a temperature greatly above that 

 of the environment is constantly maintained. Once 

 more, there is the still larger quantity of motion embodied 

 by the water that permeates organic matter. It is this 

 which, giving to the water its high molecular mobility, gives 

 mobility to the organic molecules partially suspended in it; 

 and preserves that plastic condition which so greatly facili- 

 tates re-distribution. 



From these several statements, no adequate idea can be 

 formed of the extent to which living organic substance is 

 thus distinguished from other substances having like sen- 

 sible forms of aggregation. But some approximation to such 

 an idea may be obtained by contrasting the bulk occupied 

 by this substance, with the bulk which its constituents would 

 occupy if uncombined. An accurate comparison cannot be 

 made in the present state of science. What expansion 



