THE ORIGIN OF LIFE. 2$ 



pulses all doubtless come in this category. Indeed, 

 all manifestations of the body which can be matched 

 by any machine will unhesitatingly be set down as 

 coming under the head of transformed physical 

 forces. We can believe that the body will do any- 

 thing that a machine can do without calling in the 

 aid of any distinct force. In other words, the 

 activities of living things, though more complex, are 

 as truly due to physical and chemical forces as those 

 of a machine. 



It is when we come to the other properties of life 

 not found in machines that the problem becomes 

 more difficult. No machine has the power to assimi- 

 late food and grow. These properties, which really 

 are one, form the second character which universally 

 distinguishes living matter from non-living matter. 

 Now, so far as the mechanical process of growth is 

 concerned, it is simply chemical change. This is cer- 

 tainly so in animals. They take into their body certain 

 complex substances as food. This food undergoes 

 chemical changes, chiefly those of oxidation. As a re- 

 sult, decomposition products are obtained, and some 

 of these products of decomposition are ejected, while 

 others are retained in the body, and thus the body 

 grows. But it is not quite so simple as this, for, as 

 we have seen, a certain part of the changes are con- 

 structive. Some of the decomposition products of 

 the food are united together into more complex 

 compounds, and all of it is more or less altered, so 

 that none of the food is retained in the body in 

 exactly the same condition in which it was taken. 

 In short, the body assimilates its food, converting it 



