96 TOBACCO LEAF. 



ing the process there is a large decrease in the dry mat- 

 ter of the leaf, as well as in the water. The starch is 

 turned to glucose, and the latter passes back into the 

 veins, midrib and stem, and is finally destroyed there 

 and breathed off as carbonic acid gas and water, owing 

 to an abnormally increased respiration. There is no 

 loss of nitrogen, either in the form of nicotine, nitric 

 acid or albuminoids ; the latter compounds are, however, 

 largely split up with the resultant formations of aspara- 

 gine and other amides, a change similar to that which 

 occurs whenever leaves are for a long time shaded, or to 

 that observed in the process of ensilage. Mere drying, 

 and the slow oxidation caused by the direct action of 

 the oxygen of the air, do not suffice to explain these 

 changes. They are the result of life action. 



It is not probable, though, that the lower organisms 

 are important in the normal curing process. Behrens 

 remarks,* "micro-organisms were not found in an active 

 condition upon the curing leaves, and their development 

 upon the surface of the leaves, the sole point open to 

 their attack, is rendered well-nigh impossible, owing to 

 its dryness, to say nothing of the general dry condition 

 of the inner tissues." 



The changes occur only while the protoplasm of the 

 leaf cells retains life. If the leaf be frozen, or chloro- 

 formed, the protoplasm is killed, and no normal curing 

 can be effected thereafter. Evidently, the changes ob- 

 served during the curing are due to an abnormal action 

 of the dying protoplasm of the leaves themselves ; and 

 bacterial aid offers no advantages. 



During this process, however, the lower organisms 

 sometimes act injuriously. "Pole-burn" is prevalent 

 during warm, damp, foggy weather; in a few hours, 

 the whole crop may be turned to a dark brown, wet, 



*Loc. cit., p. 286. 



