INTRASPECIFIC VARIATION ADULT PIGMENTS 321 



requires further investigation. The present position, where data 

 obtained with a particular experimental method cannot be compared 

 with those obtained by other methods, in the same species, and vice 

 versa, is unsatisfactory. 



6.2. Intraspecific Variation — Adult Pigments 



6.2.1. Methods. At least five independent lines of evidence have 

 led to the conclusion that intraspecific differences exist. These are: 

 (a) differing degrees of alkali resistance; (6) differences in elementary 

 composition; (c) different affinities for oxygen or different equilibrium 

 constants for the partition between carbon monoxide and oxygen; 

 (d) significant spectroscopic differences; and (e) differences in electro- 

 phoretic mohWity (1638,2229). It can be seen from the previous 

 sections however, that the problem is more complicated than most 

 workers have realized. If the blood pigment of an individual con- 

 tains more than one species of hemoglobin, differences between indi- 

 vidual bloods may be due to the mixture of the same components in 

 different proportion, rather than to genuine differences between the 

 composition of components that are homogeneous when tested by 

 electrophoresis, amino acid composition, or solubility. Finally, intra- 

 specific differences may be due to differences in the environment of 

 the pigments, as discussed in Section 7. 



6.2.2. Alkali Resistance. Investigation of the alkali resistance or 

 of the spreading velocity during the growth of the young animal 

 after birth has shown that considerable time may elapse before the 

 complete disappearance of the fetal pigment. The method is hardly 

 capable of doing more than this. Using these techniques, Brinkman 

 and Jonxis (336) claimed that, while in the adults of other genera 

 only one pigment is found after the disappearance of the fetal pigment, 

 in humans two adult forms were present. The fetal pigment is 

 replaced by the less resistant adult hemoglobin at seven months, 

 while the resistant adult hemoglobin does not make its appearance 

 until the third year and remains thereafter. Ramsey {2203), on the 

 other hand, claimed that two hemoglobins, differing in alkali resist- 

 ance, occurred in the blood of many vertebrate species, and that 

 the more highly developed species contained a smaller proportion of 

 the more resistant hemoglobin (c/. also Geiger, 985). 



6.2.3. DiflFerences in Composition. Many of the differences claimed 

 between the chemical composition of the globins in different individuals 



