THE COMPONENTS OF PLANTS AND ANIMALS 27 



As a rule, the vegetable proteins contain a higher percentage 

 of nitrogen than do the animal proteins. 



45. Structure of the proteins. The molecular structure of 

 the proteins is very complex and their molecular weights are 

 very large, but as yet no very satisfactory determinations of the 

 latter magnitude have been made. Determinations of the 

 molecular structure of haemoglobin (a conjugated protein) by 

 two methods have given concordant results indicating a mini- 

 mum molecular weight of 16,666, from which has been computed 

 the formula C7 5 8H 12 o3Ni95FeS2. Confirmation of this result has 

 been reported as the result of determinations of its osmotic 

 pressure. 2 For the globin of haemoglobin, a minimum molecu- 

 lar weight of between 5000 and 8000 has been obtained. For 

 serum albumin, the figure 10,166 is reported, for egg albumin, 

 5378, and for edestin 14,500. These figures are of value, how- 

 ever, chiefly as showing the complex nature of the protein mole- 

 cule. 



Up to within a comparatively few years, general statements 

 like those just made marked the limits of our knowledge of the 

 chemical nature of the proteins. The masterly researches of 

 Emil Fischer, however, and especially his creation of new 

 experimental methods, have resulted in a very great advance 

 in knowledge, and to-day, thanks to his labors and those of a 

 large number of investigators in applying and improving his 

 methods, we possess a fairly definite general conception of the 

 structure of the protein molecule. As in the investigation of 

 chemical compounds in general, two lines of attack have been 

 followed, viz., a study of the products resulting from the 

 splitting up of the molecule and attempts to synthesize the 

 compound from simpler substances of known composition and 

 structure. 



1 Four to five per cent in keratins. 2 Zentbl. Physiol., 21, 730. 



