48 BlILDING OF THE LIVING MACHINE 



or more amino-acids. Of these substances, glycerose is 

 one of the very simplest sugars known, and lactic acid 

 is a common organic acid, formed for example in the 

 souring of milk (see Chap. XXIII). The amino-acid, 

 alanin (C3H7NO,), commonly formed in the hydrolysis 

 of proteins, serin (C3H7NO3), a somewhat less simple 

 compound, and cystein (C3H7NO2S), particularly inter- 

 esting as containing sulphur, may be arranged in a series, 

 (with glycerose and lactic acid), as proposed by Abder- 

 halden, thus: 



glycerose — ^ lactic acid — > alanin — » serin — > cystein —> protein 

 CHO CH3 CH3 CH2OH CH2SH 



II 111 



CHOH CHOH CHNH2 CHNH2 CHNH2 



I r I I I 



CH2OH COOH COOH COOK COOH 



If phosphorus is added to the protein molecule there re- 

 sults a nucleo-protein. The nucleo-proteins are the most 

 complex substances known. 



The Organization of Protoplasm. — The protoplasm 

 of the cell consists of two different parts, cytoplasm and 

 nucleus. The latter will be discussed more fully in a 

 later chapter (XXV) and so may be dismissed here 

 with a bare mention. The cytoplasm exists in two dif- 

 ferent conditions, according to the relations of its various 

 components to one another. In one condition it is fluid 

 and capable of flowing movements; in the other it forms 

 a more or less finn. jelly-like structure. In the liquid 

 condition, water containing salts in true solution consti- 

 tutes a continuous phase in which the colloidal particles 

 of protein, oil. and other substances are in suspension 

 or in colloidal solution. In the firmer condition the 

 protein particles coalesce to form a continuous phase 

 which encloses minute drops of water and dissolved salts 

 as well as ultramicroscopic drops of oil and fats. Which 

 of these two conditions will exist at any given time de- 



