28 BULLETIN 19, U. S. DEPARTMENT OP AGRICULTURE. 



Considering collectively the changes in the various constituents 

 involved in curing, we find in the case of the primed leaves that, 

 where the analyses are complete, the sum of the various losses 

 recorded, less the sum of the gains, gives a total loss amounting to 

 from 70 to 90 per cent of that obtained in Table I; or, in other words, 

 our analyses have accounted for this proportion of the constituents 

 which are of importance from a quantitative standpoint. A very 

 close agreement is not to be expected, since the factors used in cal- 

 culating the protein and the amid and amido constituents are probably 

 only approximately correct. The results of the analyses account for 

 about 75 per cent of the loss in weight indicated in Table I, where 

 the leaves are cured on the stalk. 



Aside from the observations made by Muller-Thurgau regarding the 

 loss of starch and sugars in the curing, which have already been men- 

 tioned, the only paper bearing directly on the changes in composi- 

 tion during the curing, so far as known, is that of Behrens, 1 who, like 

 nearly all previous investigators, was concerned mainly in a compari- 

 son of the methods of curing on the stalk and of curing the primed 

 leaves. He presents data, however, showing the comparative com- 

 position of green and cured leaves. Since the total loss of weight in 

 curing was not determined, the changes in composition can only be 

 considered qualitatively. His analyses indicate the disappearance of 

 starch and a decrease in sugars and protein nitrogen in curing. 

 They show also a relative loss of total carbon and a relative gain in 

 total nitrogen during the curing process. 



While little is known as to the identity of the individual com- 

 pounds making up the groups of constituents involved in the curing 

 changes, particularly as regards the protein group and their cleavage 

 products, the general character and course of the transformations 

 concerned can be considered as definitely established. The follow- 

 ing scheme shows the general course of the changes common to both 

 methods of curing which the several groups of constituents undergo 

 during the curing process, the prime factor in effecting these trans- 

 formations being respiration, although the phenomena of transloca- 

 tion play a more or less important rdle, depending on the method of 

 curing followed. 



Diagram showing the general course of changes during the curing process. 



[Oxalic acidl 

 Starch >Sugars >\ Citric acid L (?)- -»Carbon dioxid and water. 



Pentosans. - I Malic acid J.—--" 



„-* 

 .--Cn- 

 Protem +l A f£2iE&!E' ao )- — -JcaX^dioxid. 



\ derivatives / ^Water. 



i Behrens, Johannes. Weltere Beitr&ge zur Kenntnis der Tabakpflanze. Die Landwirtschaftlichen 

 Versuchs-Stationen, Bd. 43, p. 271-301, 18 



