286 LECTURE XIII. 



midine bases are synthetically formed by the cells for this purpose. To be 

 eure, the animal organism at least, that of the birds and the reptiles is 

 capable of building up uric acid. From the whole manner of its formation 

 it would seem very improbable that the purine bases have the same origin. 

 In this connection we must indeed recall the work of F. Knoop and 

 A. Windaus, 1 from which we can easily assume a synthetic production of a 

 compound which is important to the cell-metabolism. These two inves- 

 tigators have shown that the action of ammoniacal-zinc-hydroxide on 

 grape-sugar in the cold produces an oxygen-free base in large quantity; 

 namely, methyl-imidazole : 



CH 3 C NH 



)CH 

 CH-N 



This gives us a connecting link between the carbohydrates and the 

 purine bases. It is possible that analogous reactions may occur in the 

 plant organism. The animal cell would hardly look to the carbohydrates 

 as a source for the production of nitrogenous material; at least, nothing 

 at present known would indicate that it does. We will state here that, 

 in spite of. the large number of recent observations in the field of purine 

 metabolism, it is still impossible for us to give an exact account of the 

 influence of this class of bodies on the total metabolism, and even less so 

 in the case of the nucleoproteids and nucleic acids in the individual cells. 

 We know that the animal organism utilizes materials containing purines 

 for its requirements. There are nutrient substances, like meat, rich in 

 purine bases, and others, again, containing less of these. Milk belongs to 

 the latter class. The animal cell undoubtedly requires nucleic acid and 

 also purine bases for the purpose of building up nucleoproteids. They con- 

 stantly decompose as we shall soon see those constituents which contain 

 purine and replace them again. From this we can easily imagine that the 

 cell utilizes the nucleic acids either in their original or converted form to 

 replace wasted material or to construct new cells. We shall see later that 

 the animal organism continues to break down material containing purines, 

 even in cases of extreme starvation, some of the derivatives formed by 

 this process appearing in the urine. There is a far-reaching analogy here 

 to the behavior of the proteins in the organism. It is possible in fact 

 very probable that the nucleoproteids in the form of nucleic acids are 

 utilized by the cells, at least in part, in the manner just indicated. We 

 must not forget, however, that we have no absolute proof of this. In fact 

 there are some observations which point to the probability that the animal 

 organism, like the plants, is also capable of directly synthesizing the purine 



1 F. Knoop and A. Windaus: Ber. 36, 1166 (1905). Hofmeister's Beitr. 6, 392 (1905V 



