108 PHYSIOLOGICAL ACTIVITIES 



sources of nitrogen. Most of these experiments were disap- 

 pointing. Plant proteins are not so different from animal 

 proteins, or plant protoplasm (apart from the chlorophyl 

 portions of plants) from animal protoplasm as to lead one to 

 suppose that it could be built up from one or two amino- 

 acids any more than animal protoplasm can. The author 

 is strongly convinced that this subject should be thoroughly 

 investigated. It will require careful experimentation and 

 perhaps rather large funds to provide the amounts of amino- 

 acids that would probably be needed, but might result in a 

 decided change in om- ideas of soil fertility, and especially 

 in the use of nitrogen fertilizers. 



