J. H. P. JONXIS 



molecular layer and the dissociation curve of the foetal haemoglobin 

 is shifted to the left. This makes it probable that a lower resistance 

 against alkali goes with an easier unfolding of the molecule and a 

 higher affinity for oxygen {Table I). The parallelism between the easy 

 unfolding of the molecule and the low resistance to alkali may be 

 explained by the fact that in the less resistant forms of haemoglobin 

 the bindings are less solid between the 4 parallel layers of polypeptide 

 chains of which the human haemoglobin molecules may perhaps be 

 built up (by analogy with horse haemoglobin which is believed to 

 have this structure). In the more resistant forms, the affinity for 

 oxygen is less. 



Table I 



Man 



Cow, Sheep, Goat 



Adult Hb Foetal Hb Adult Hb Foetal Hb 



Alkali 

 resistance 



Unfolding 

 on trough 



low 



high 



high 



rapid 



slow 



slow 



low 



rapid 



Dissociation 

 curve 



shifted to 

 the right 



shifted to 

 the left 



It is known that in many children a small proportion of later 

 haemoglobin is already present at birth. During the following months 

 of life the percentage of foetal haemoglobin diminishes constantly 10 ' 11 . 

 I have made a number of determinations to see how long it takes for 

 the last traces of foetal haemoglobin to disappear. The results are 

 shown in Figure 4. At birth the percentage of later haemoglobin in 

 healthy children varies between 2 and 25 per cent. The percentage 

 of foetal haemoglobin decreases gradually : it is never found in 

 children older than 22 weeks. There are great individual differences. 

 In healthy children who are rapidly gaining weight the foetal haemo- 

 globin diminishes more rapidly than in dystrophic children. When 

 there is a considerable breakdown of haemoglobin during the first 

 days of life the percentage of foetal haemoglobin decreases propor- 

 tionately. It is clear that the breakdown of the haemoglobin in these 

 cases occurs at the expense of the foetal haemoglobin and one can 



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