CHAPTER II. 



THE ALBUMINS 



THE albumins, or proteins, are the most important food-stuffs 

 which the animal requires for its existence. They play a pre- 

 dominating role in the construction of all the tissues and organs of 

 the body, and form the groundwork of every living cell. The 

 phenomena of life depend upon and centre in their presence. 



While many different forms of albumins exist, they all present 

 certain general chemical and physical characteristics, which serve 

 to distinguish them as a class, and which show that a close genetic 

 relationship exists between them. 



Elementary Composition. All albumins contain carbon, hydro- 

 gen, nitrogen, oxygen, and sulphur in certain definite proportions, 

 which vary within fairly narrow limits in the different members of 

 the group, but tell us very little, as such, of the structure of the 

 albuminous molecule. The variations which do occur are shown in 

 the following table: 



Carbon 50.0-55.0 per cent. 



Hydrogen 6.5- 7.3 " 



Nitrogen 15.0-17.6 " " 



Oxygen 19.0-24.0 u " 



Sulphur 0.3- 2.4 " " 



Other elements are not found in the common albumins, but occur 

 in certain compound albumins, which result through the union of 

 an albuminous group with other more or less complex radicles. 

 The haemoglobins thus contain iron, the nucleoproteids phosphorus ; 

 one highly differentiated globulin contains iodine, etc. All albu- 

 mins further contain variable amounts of mineral salts, which are 

 closely united with the albuminous molecule. The most important 

 and constant of these are the chlorides and phosphates of the alkalies 

 and the alkaline earths. 



The structural formula of the albumins is unknown. The mole- 

 cule is unquestionably very large. In the case of serum-albumin 

 Hofmeister calculated the general formula as C 450 H 720 N 116 S 6 O 140 , 

 which would correspond to a molecular weight of 10,166. (See 

 molecular weight and structural composition, below.) 



Reaction. In the free state the albumins are neutral ; m such 

 solutions they are not ionized, but this results at once on contact 

 with other ions. They then form salts, both with acids and bases 

 which are fairly good conductors, and thus play the part of pseudo- 

 acids and pseudo-bases (Hantzsch). As acids the albumins are 

 dibasic (Osborne, Soldner, and others). One series of salts shows a 

 neutral reaction with the usual indicators, while the other is more 



27 



