NITROGENOUS EXCRETION 



61 



of his work on the effects of amines on the nitrogenous metaboHsm 

 of tissue homogenates. No information was available to him 

 regarding the actual amines represented in the cells, but recently 

 paper chromatographic studies have been made of the chloragogen 

 cells. Cells isolated from fresh animals possess three amino-acids, 

 ornithine, glutamic acid and occasionally arginine. Glycocol and 

 kynurenine, a breakdown product of tryptophan in mammals, 

 are also found. A period of starvation leads to the disappear- 

 ance of ornithine, glutamic acid remaining and arginine being 



Fed in by Cohen and Lewis 1949 



Citrulline + aspartic acid W) 



Ornithine U) 



Arginosuccinic 

 acid 



Arginase (V) 



Urea W) 



Arginine W) 



Fed in by Cohen and Lewis 1949 



Fig. 20. Ornithine Cycle indicating components demonstrated as 

 being present in or having an effect when fed to earthworms. 



found now in all the animals studied instead of one or two. 

 Citrulline is not present at either stage. The Krebs-Henseliet 

 cycle of reactions (Fig. 20) involves the interaction of ornithine, 

 arginine and citrulline. Glutamic acid is rapidly interchangeable 

 with aspartic acid in mammals, but this reaction has not been 

 shown in annelids. It also, by reason of combining with ammonia 

 to form glutamine, can act as a carrier for this toxic waste product. 

 It can thus be seen that part of the cycle is present, but the 

 absence of citrulline is confusing, especially so since Cohen and 

 Lewis (1949b) report that the urea production of the earthworm 



