330 VII. COMPARATIVE BIOCHEMISTRY OF HEMOGLOBINS 



pregnancy. The difference between the blood and the purified hemo- 

 globin in fetus and mother is not only in the same direction but is of 

 the same magnitude. Hall {1106), working with a spectroscopic 

 method {1105) which enabled him to work with blood diluted hundred- 

 fold, found that, at 32° C. and pW 6.8, the saturation of the fetal 

 and maternal pigments in the goat at fifteen weeks' gestation was 72 

 and 53%, respectively at 30 mm. mercury. In addition, he found 

 the fetal curve to be shifted to the left of the maternal curve in the 

 rabbit. In comparison with McCarthy's data. Hall's results show 

 that in dilute solution, both the maternal and the fetal pigment 

 have a greater aflSnity for oxygen than in stronger solution. Hauro- 

 witz {llGJt) and Hill and Wolvekamp {1286), the latter workers 

 using dilute solutions, found, however, that in the hemoglobin of the 

 human species, the relative positions of the two curves were reversed, 

 the fetal pigment having a smaller affinity for oxygen than the 

 maternal pigment. The problem was reinvestigated by McCarthy 

 {1801), who confirmed these results for both dilute and concentrated 

 solutions of maternal and fetal hemoglobin. He also confirmed the 

 earlier work done on the whole blood of mother and fetus. 



The above results show the operation of generic factors in the 

 functional adaptations of the fetus to its intrauterine existence. In 

 the goat, the increased aflSnity of the fetal pigment is apparently 

 determined by the structure of the hemoglobin; the microenvironment 

 plays little or no role. In humans, the adaptation is achieved solely 

 by the chemical influence of the erythrocyte on the hemoglobin. 

 The chemical differences which exist between the maternal and fetal 

 hemoglobins in humans are not able, by themselves, to produce the 

 necessary functional adaptation. 



10. FUNCTIONAL ADAPTATION — MYOHEMOGLOBIN 



While the early, work of Barcroft led to the division of the oxygen 

 carriers into oxygen transporters and oxygen stores {139,14^1), it was 

 not until the much greater affinity of myohemoglobin for oxygen was 

 discov^ered that its function as an oxygen store rather than as an 

 oxygen transporter was realized {1^2). Millikan {1951}.) summarizes 

 the qualifications for an effective store as a pigment which has suffi- 

 cient capacity, suitable loading and unloading tensions, and is able 

 to load and unload its oxygen with sufficient speed. 



In the dog, the myohemoglobin content of heart muscle is about 



