REQUIREMENTS FOR HEMOGLOBIN SYNTHESIS 607 



to a physiologically increased breakdown of hemoglobin {cf. Chapter XI, 

 Section 6.5.) and partly owing probably to an exhaustion of iron reserves 

 and a poor supply of iron in the milk. It seems to be significant that the time 

 at which the minimum occurs has been found consistently shorter in more 

 recent researches {240o,240S) than previously, probably because of the 

 earlier supply to the baby of food rich in iron. Later the hemoglobin rises 

 gradually to the adult level, the sex difference appearing only in the period 

 of puberty. 



3. REQUIREMENTS FOR HEMOGLOBIN SYNTHESIS 

 IN THE ANIMAL BODY 



3.1. Introduction 



It is a difficult task to establish with certainty the significance of 

 a given factor for hemoglobin synthesis. What is usually measured 

 is the variation in hemoglobin concentration in the blood caused by 

 the lack of a certain factor in the food or by its administration in 

 excess. The difficulties involved in altering the supply of one factor 

 without simultaneously altering others, some of which may be still 

 unknown, have only gradually been overcome. If we neglect possible 

 alterations in blood volume, the hemoglobin concentration depends 

 on the balance of formation and destruction of hemoglobin; conse- 

 quently before the absence of a factor can be said to diminish hemo- 

 globin synthesis, it must be shown by measurement of bile pigment 

 excretion that a decrease of hemoglobin is not due merely to increased 

 destruction. 



Even if all this has been accomplished, the problem is far from 

 being solved. In Section 1. we have pointed out the difficulty of 

 deciding whether a certain factor is required for the synthesis of 

 hemoglobin or for the formation of the erythrocyte. It is also often 

 difficult to decide whether a factor which by its chemical structure 

 may be supposed to be required as a building stone of the hemoglobin 

 molecule is actually required for this purpose, or whether it influences 

 hemoglobin synthesis in an indirect way. There are varying degrees 

 of indirectness in such a stimulating action. The substance may act 

 as a catalyst of the intracellular hemoglobin synthesis itself, or of the 

 formation of precursors in the cell or elsewhere. It may act upon 

 another factor necessary for this synthesis, such as iron, by influencing 

 mobilization from the depots or absorption from the intestine. Even 

 more indirectly, it may influence the oxygen supply of the bone 



