322 BIOLOGY 



SUMMARY 



1. All physical energy exerted by the living organism is 

 distinctly correlated with other forms of energy, the energy of 

 plants coming from sunlight, and that of animals coming from 

 the energy stored by plants in their foods. To this extent, 

 therefore, a living organism is a machine. 2. Nearly all life 

 functions are explainable by chemical and physical laws. This is 

 certainly true of such functions as digestion, assimilation, circu- 

 lation, excretion, respiration, etc. 3. Some of the functions of 

 the living animal are not yet explained by chemical or physical 

 forces. This is true of the absorption of the food from the 

 intestines, and the power which the living cells have of taking 

 from the lymph the particular form of food that they need. 

 We may gather these factors for the present under the term 

 "vital forces" of the living organism. After we have learned 

 thoroughly to understand them and their method of action, 

 we may find these processes are also to be included under the 

 general laws of physics and chemistry. There is really no good 

 reason for questioning that the living organism is a mechanism, 

 simply because there are some functions which are at present 

 unintelligible. 4. In the mental power of the living organism 

 appear functions which are not found in any machine. The 

 functions of mind, sensation, and thought are so absolutely 

 unique, and so different from any other type of energy, that 

 no one has ever conceived the possibility of correlating them 

 with physical energy. 5. Only the living machine has the 

 power of reproducing itself. It is true that some forms of the 

 process of reproduction may be explained simply as a result 

 of growth, and growth as due to the chemical forces that are 

 at play within the living organism. But it nevertheless remains 

 true that no other mechanism in nature has the power of divid- 

 ing itself into two parts, each of which develops into an indi- 

 vidual like the first. Taking all these things into considera- 

 tion, it is evident that, so far as physical forces are concerned, 

 the living organism is a machine, and, like other mechanisms, 



