806 THE ROLE OF NITROGEN, ETC., I., 



as a reversible enzyme-reaction, and that enzymes are directive 

 agents in building up both starch and oils, even cellulose and 

 glucosides. 



(b) Relation of Carbohydrates to Fats. — The role of fats in the 

 plant has been shown to he similar to that of the carbohydrates; 

 both are reserve-materials found together, and serve the same 

 purpose in metabolism. They are capable of being transformed 

 into one another by the protoplasm (9) — carbohydratezztfat. It 

 has been observed in certain plants that inulin, starch, glucose, and 

 fat are formed in succession from the same food-substances. (9) 

 Again, Sachs observed that fat was formed from glucose in the 

 ripening seeds of Ricinu.s, and Pfeffer that the starch in the 

 endosperm of Pseonia was converted into fats. All oily seeds, 

 when unripe, contain much starch, and as they ripen the forma- 

 tion of oil may be observed; when the seeds are ripe the starch 

 may be wholly replaced by fatt} r oil. (9) 



Conversely, in germinating seeds fat is changed into carbo- 

 hydrate. A. Fischer(lO) has pointed out that temperature is an 

 important factor in these changes; he has noted, for example, the 

 change of starch into fat in trees in the winter, and the reverse 

 taking place in the spring. That these changes take place in the 

 plant there is little doubt, though the evidence rests entirely on 

 physiological experiments, and the exact chemical course which 

 is followed has not yet been explained. The conversion of 

 carbohydrate into fat was first suggested by Liebig, and after- 

 wards proved by the historic experiments of Gilbert and Lawes 

 at Rothamsted. 



It is of interest here to glance briefly at the mechanism of 

 certain processes whereby this end is achieved in synthetic 

 chemistry. Sugars are readily converted into lactic acid by 

 weak alkalies, (11) and by the enz}-mes of micro-organisms and 

 yeast,(12). C,.H 12 6 = 2C 3 H 6 3 . One of the general properties 

 of lactic acid is its decomposition to aldehyde and formic acid; 

 aldehyde is exceedingly liable to condense into aldol, and aldol 

 reacts with water to yield fatty acids. (13) Hoppe-Seyler con- 



