26 INTRODUCTION. 



Synthesis of the Albumins. Much more complicated than the 

 synthesis of the carbohydrates and fats is that of the albumins, 

 a class of bodies which occur widely distributed in both the animal 

 and the vegetable world, and form the groundwork, so to speak, of 

 all living matter. Like the carbohydrates and fats, they also con- 

 sist of carbon, hydrogen, and oxygen, but in addition to these ele- 

 ments nitrogen and variable amounts of sulphur are constantly 

 present. To this class belong such bodies as serum-albumin, egg- 

 albumin, casein, fibrin, etc. They are exceedingly complex sub- 

 stances, and have a very high molecular weight. 



The exact manner in which the albumins originate has not been 

 determined. We are in possession of a number of observations, 

 however, which permit some insight, at least, into the manner in 

 which plants are capable of elaborating these complex substances 

 from the simple material which serves as their food, and there is 

 reason to suppose that the synthesis of the albumins also takes 

 place, to a certain extent at least, in the chlorophyl-bearing por- 

 tions of plants. 



It was formerly supposed that the nitrogen necessary in these 

 synthetic processes was furnished plants in the form of ammonium 

 salts. Subsequent investigations have shown, however, as has been 

 indicated, that this is usually not the case, and we now know that 

 through the activity of various bacteria in the soil the nitrogen 

 required by plants is here oxidized to nitrates. These are absorbed 

 and carried to the chlorophyl-bearing portions of the plant, where, 

 as we have seen, formic aldehyde and glucose are constantly being 

 formed. Here, or in the rootlets, a certain proportion of the nitrates 

 is apparently transformed into nitric acid, which is then promptly 

 reduced by the formic aldehyde, with the formation of a certain 

 amount of hydrocyanic acid, as shown in the equation : 



2HN0 3 + 5CH 2 O = 2HCN + 3CO 2 + 5H 2 O. 



In this form, then, the nitrogen probably enters into the construc- 

 tion of the albuminous molecule. This supposition is strengthened 

 by the observation that hydrocyanic acid, as such, or in the form of 

 cyanides, occurs widely distributed in the vegetable world, and is 

 characterized by the readiness with which it combines with a large 

 number of organic substances to form highly complex chemical com- 

 pounds. The nature of the subsequent changes will be better under- 

 stood when the decomposition-products of the albumins have been 

 studied in detail. These will be considered in a following chapter. 



