Studies on Mammalian Red Cells 



71 



Neuberger and Perrone, 1951). The curves obtained differ 

 markedly from those observed in man. The isotope content 

 of the porphyrin rose sharply from the 10th-40th hour after 

 injection and a maximum was usually observed between the 

 fourth and the sixth day, but occurred sometimes on the tenth 

 day of the experiment. In some of the rabbits there was a 

 plateau between the 10th and 30th day, but in most animals 

 there was an almost linear decrease from the 10th-12th day 



-40 60 80 100 120 140 160 



DAYS AFTER ADMINISTRATION OF GLYCINE 



Fig. 1. ^^N content (atom per cent excess) of haemin samples 



obtained at various times from a rabbit (3-2 kg. body wt.) which 



had received 3-5 g. of glycine containing 30-5 atom per cent 



excess ^^N. Broken line corrected for loss of blood. 



onwards, similar to that found in haemolytic ansemias in man. 

 The isotope content of the haem had generally fallen to half 

 its maximum value by about the 50th day. In most rabbits 

 the rate of decrease after the 50th day slowed down con- 

 siderably, and there was still about 15 per cent of the maxi- 

 mum isotope content present in the haem 160 days after 

 feeding isotopic glycine (Fig. 1). The main difficulty in these 

 experiments is that the withdrawal of blood required for 

 isotope analysis may bring about a secondary anaemia and 

 thus affect the results. In order to minimize this danger, we 



