CHEMIC COMPOSITION OF THE HUMAN BODY 13 



Chemic Composition. A chemic analysis of proteins shows that 

 they consist of carbon, hydrogen, oxygen, nitrogen and sulphur, though 

 the percentage of each of these elements varies somewhat in the different 

 proteins. 



A certain number of proteins contain phosphorus while almost all 

 of them contain different inorganic salts in varying amounts. The average 

 percentage composition of several proteins is shown in the following analyses: 



C. H. N. O. S. 



Egg-albumin 5 2 -Q 7.2 15.6 23.9 0.4 (Wurtz). 



Serum-albumin 53 - 6.8 16.0 22.29 1.77 (Hammersten). 



Casein 52.3 7.07 15.91 22.03 0.82 (Chittenden and Painter). 



Myosin 52.82 7.11 16.77 21.90 1.27 (Chittenden and Cummins). 



The molecular composition of the proteins is not definitely known 

 and the formulae which have been suggested are therefore only approxi- 

 mative. Leow assigns to albumin the formula C 72 H 112 N 18 O 22 S, while 

 Schiitzenberger raises the numbers to C 240 H 392 N 65 O 75 S 3 , either of which 

 shows that the protein molecule is extremely complex. 



Structure of the Protein Molecule. From the large size of the protein 

 molecule as indicated by its chemic composition it might be inferred that 

 its structure was equally complex. This, modern investigation has shown 

 to be the case. 



When any one of the typical proteins, found in animal or vegetable 

 tissues, is hydrolyzed by acids, alkalies and animal ferments under appro- 

 priate conditions, it can be resolved through a series of descending stages 

 into simpler bodies, represented in the early stages by proteoses, peptones, 

 and peptids. Under the continued action of the hydrolyzing agent, the 

 peptids are reduced to relatively simple nitrogen-holding bodies termed 

 amino-acids and diamino-acids, of which somewhat more than twenty have 

 been isolated and their properties determined. The principal amino-acids 

 are as follows: Glycocoll, alanin, leucin, isoleucin, amino-isovalerianic 

 acid, serin, aspartic acid, glutamic acid, phenylalanin, tyrosin, prolin, 

 tryptophan. The principal diamino-acids are as follows: Ornithin, lysin, 

 histidin, arginin, cystin. 



The protein molecule is therefore structurally complex. The manner 

 in which these elementary compounds are arranged, united or grouped 

 in any given protein, is practically unknown. More or less successful 

 attempts have been made at the reconstruction of the protein molecule by 

 synthetic methods, by the union of two or more of the amino-acids. A 

 number of such compounds have been formed by the union of from two to 

 ten or more amino-acids, all of them exhibiting many of the protein reac- 

 tions. Such bodies are termed, according to their complexity, di, tri, 

 tetra, and pentapeptids and polypeptids. 



Physical Properties. As a class the proteins are characterized by the 



following properties: 



i . Indiff usibility . None of the proteins normally assume the crystalline 

 form, and hence they are not capable of diffusing through parchment 

 or an animal membrane. Peptone, a product of the digestion of 

 proteins, is an exception as regards its diffusibility. As met with in 

 the body, all proteins are amorphous, but vary in consistence from the 



