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these momentous facts is that soon all the world's supply of com- 

 bined nitrogen would be exhausted — neglecting the relatively- 

 small replenishment induced by cosmic forces — so that green 

 plants and consequently animals, would not have the wherewithal 

 to live, unless there were some organisms which could avail 

 themselves directly of this inert gas. Now there are plant or- 

 ganisms which have the ability to assimilate the uncombined 

 nitrogen of the air : certain bacterial forms, and it also appears 

 some somewhat higher plants. But the operations that lead to 

 this result are by no means satisfactorily explained, and the 

 whole topic is one of live interest both from a theoretical as well 

 as a practical standpoint. It should be added that from the 

 latter point of view, a process by which a combination of nitro- 

 gen with other elements in a form that is acceptable to green 

 plants has been devised, and bids fair to become of great impor- 

 tance, for combined nitrogen is the great need of the organic 

 world. 



The processes of nitrification naturally lead us to the question 

 of the elaboration of nitrogen compounds within the cell, of the 

 final construction of proteid material that is the actual food of the 

 protoplasm ; but here we are much in the dark, partly because 

 we have so little real information as to the chemical structure of 

 the more complicated nitrogenous substances. The explanations 

 now given as to how this elaboration takes place are largely 

 hypothetical and must be regarded as quite unsatisfactoiy. 



A step further from the proteid food is the question of living 

 protoplasm itself, and one of the most interesting problems con- 

 nected with this is the nature and functions of the enzymes, — 

 the ferments and digestive secretions of living cells. Many of 

 the newer theories as to the nature of living protoplasm hark back 

 to investigations regarding enzymes, indeed some extremists ad- 

 vance the opinion that the activities of the live protoplast are in 

 themselves but the result of the interaction of substances enzy- 

 matic in their nature. There is no doubt of the power of the 

 appropriate enzymes when present even in infinitesimal amount 

 to cause enormous molecular changes in the substances on which 

 they act, but it is necessary to exercise extreme caution before 



