CHAPTER VI. 



FERMENTATIONS AND THE ACTION OF 

 ENZ YMES ( Continued). 



I. Proteins. Proteins are among the most important 

 compounds present in the tissues of animals and plants. 

 The majority are exceedingly complex in chemical consti- 

 tution, and although our knowledge of them has been 

 greatly advanced during the last few years by study of 

 their decomposition products, much remains to be done 

 before the exact nature of these substances is understood. 

 Protoplasm, the peculiar material in the cells of living 

 organisms, with which the phenomena of life are 

 mysteriously associated, consists of an unstable mixture 

 of proteins. They are also found in solutions, or in a 

 colloidal state in blood, lymph, milk, and similar liquids 

 obtained from organic beings. Some proteins are met 

 with in a dense semi-crystalline form in the storage 

 tissues of seeds and tubers, and others have been 

 obtained in a true crystalline state from blood, egg- 

 albumen, and certain seeds ; most of them, however, are 

 slimy, non-crystalline substances, like the white of an 

 egg, and contain nitrogen, and sulphur in addition to the 

 elements carbon, hydrogen and oxygen ; certain proteins, 

 such as the caseinogen of milk, contain phosphorus also. 

 The amount of carbon present is usually between 

 5 2 to 5 5 per cent. ; nitrogen, 1 6 to 1 8 per cent. ; hydrogen, 

 6.5 to 7.5 per cent. ; sulphur, from 2.5 to 5.3 per cent. 



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