24 REPORT — 1887. 



That this conclusion of Liebig's is correct needed experimental proof, 

 but such proof could only be given by long-continued and laborious experi- 

 ment, and this serves to show that chemical research is not now confined 

 to laboratory experiments lasting perhaps a few minutes, but that it has 

 invaded the domain of agriculture as well as of physiology, and reckons 

 the periods of her observations in the field not by minutes, but by years. 

 It is to our English agricultural chemists Lawes and Gilbert that we 

 owe the complete experimental proof required. And it is true that this 

 experiment was a long and tedious one, for it has taken forty-four years 

 to give the definite reply. At Rothamsted a plot was set apart for the 

 growth of wheat. For forty-four successive years that field has grown 

 wheat without addition of any carbonised manure ; so that the only 

 possible source from which the plant could obtain the carbon for its 

 growth is the atmospheric carbonic acid. Now, the quantity of carbon 

 which on an average was removed in the form of wheat and straw from 

 a plot manured only with mineral matter was 1,000 pounds, whilst on 

 another plot, for which a nitrogenous manure was employed, 1,500 

 pounds more carbon was annually removed ; or 2,500 pounds of carbon 

 are removed by this crop annually without the addition of any carbona- 

 ceous manure. So that Liebig's prevision has received a complete ex- 

 perimental verification. 



May I, without wearying you with experimental details, refer for a 

 moment to Liebig's views as to the assimilation of nitrogen by plants — ■ 

 a much more complicated and difficult question than the one we have 

 just considered — and compare these with the most modern results of 

 agricultural chemistry ? We find that in this case his views have not 

 been substantiated. He imagined that the whole of the nitrogen required 

 by the plant was derived from atmospheric ammonia; whereas Lawes 

 and Gilbert have shown by experiments of a similar nature to those just 

 described, and extending over a nearly equal length of time, that this 

 source is wholly insufficient to account for the nitrogen removed in the 

 crop, and have come to the conclusion that the nitrogen must have been 

 obtained either from a store of nitrogenous material in the soil or by 

 absorption of free nitrogen from the air. These two apparently contra- 

 dictory alternatives may perhaps be reconciled by the recent observations 

 of Warrington and of Berthelot, which have thrown light upon the 

 changes which the so-called nitrogenous capital of the soil undergoes, as 

 well as upon its chemical nature, for the latter has shown that under cer- 

 tain conditions the soil has the power of absorbing the nitrogen of 

 the air, forming compounds which can subsequently be assimilated by the 

 plant. 



Touching us as human beings even still more closely than the fore- 

 going, is the influence which chemistry has exerted on the science of 

 pathology, and in no direction has greater progress been made than in 

 the study of micro-organisms in relation to health and disease. In the 

 complicated chemical changes to which we give the names of fermentation 



