THE PROTOPLASMIC SYSTEM 



tissues. Thus, not the elements as such characterize the 

 structure of living matter but the peculiar combination of 

 elements which constitute the protein, the lipin and the 

 carbohydrate molecules of living matter. 



These compounds are suspended and dissolved in an 

 aqueous medium containing electrolytes as Na, K, Ca,Mg, 

 CI, etc., with oxygen and carbon-dioxide. The whole mass 

 of protoplasm — organic compounds, electrolytes, water and 

 gases — it seems, maintains a fairly constant slightly alkaline 

 reaction. 



Each of the three organic compounds is built up of 

 simpler molecules strung together: the proteins are strings 

 of amino acids formed in some such manner as the following: 



C4H9.CH(NH2).CO.NH.CH2.CO.NH.CHo.COOH 



which is a poly-amino-acid or tripeptide of leucin: 



CH3CH.CH2.CH(NH2)COOH 



and two molecules of glycin: 



CH3CH2.NH2.COOH 



The more complex proteins show comparable linkage.^ 



The lipins, as shown by the chemical structure of a simple 

 fat, are combinations of three molecules of fatty acid and 

 one of glycerol, as : 



CH3.CH2.CH2.COOH + CH2.OH 

 CH3.CH2.CH2.COOH + CHOH 

 CH3.CH2.CH2.COOH + CH2.OH 

 with the loss of three molecules of water. 



Monosaccharides (simple sugars), disaccharides (second- 

 ary sugars) and polysaccharides (starches and the like) 



^ With the aid of the ultra-centrifuge and by means of x-ray- 

 spectroscopy valuable information is to-day being gathered con- 

 cerning the protein-molecule . 



39 



