i6 ELEMENTS OF BIOLOGY 



stances may be, and in many cases have been studied by the chemist. 

 But none of these are aUve when isolated from protoplasm, although 

 they behave in the test tube much as they are known to behave in 

 the living material. 



Life as a Chemical Process. Of the many types of com- 

 pounds that occur in protoplasm, some react readily, some are 

 loosely bound, unstabile molecules, some are inert, and some are 

 stabile. A number of simple chemical reactions have been given 

 here to illustrate the principles. In the living organism some of 

 the reactions are similarly simple; others are exceedingly complex, 

 for example, changes and re-combinations in the proteins. In 1828 



Wohler artificially manufactured urea (CO\' njlj^ ) ; it was the first 



of the so-called organic compounds to be synthesized artificially. 

 This led to the study and synthesis of other organic compounds and 

 gave impetus to the idea that life is a chemical process. It was rea- 

 soned that since protoplasm was made up of organic and inorganic 

 compounds and continues always to build up these substances, life 

 itself must be a series of chemical reactions. This led further to the 

 idea that protoplasm is alive because it may be composed of a 

 peculiar type of organic molecule; the expression "the living mole- 

 cule" is still occasionally used. But the living properties of proto- 

 plasm are not identical with the properties of any single type of 

 molecule found in the system; they are the products not only of the 

 chemical properties but also of the physical properties of many sorts 

 of molecules. For instance, water in protoplasm has the same prop- 

 erties that water in the stream has; proteins have the same proper- 

 ties as in a test tube. In protoplasm these properties contribute to 

 the characters of life but are not themselves life. In other words, the 

 process of living is the summation of a complex series of both physi- 

 cal and chemical events in which all compounds present take 

 part. Eventual success in artificially producing living protoplasm 

 rests entirely on the hope of being able to unravel this series. No 



