CHAPTER I 

 ^ FOOD OF MICROORGANISMS 

 The Composition of the Cell 



Cells under average conditions may contain certain compounds 

 which are in no way essential to life manifestations; they are in the 

 medium in which the cell grows, and thus pass into the cell without 

 taking part in its fimctions. Sodium and silicon are probably elements 

 of no use to bacteria though commonly present in the cells. Most of 

 the compounds of the cell are, however, essential to normal develop- 

 ment. Some idea of the needs of the cell may be obtained by studjdng 

 its composition. 



Moisture. — ^The amount of water in the cells of microorganisms 

 will vary with the species as well as with the cultural conditions. The 

 total solids of " mother-of -vinegar " are only 1.7 per cent. This should 

 be considereid as an extreme and very unusual case, owing to the spongy 

 nature of the jelly-like cell membrane. The average water content of 

 bacteria seems to be about 85 per cent; it varies more with yeasts and 

 still more -with, higher fungi. It seems reasonable to suppose that 

 organisms grown in concentrated solutions as the organisms of salted 

 meat and the molds growirig in strong sugar solutions contain more 

 sohds. Spores of molds contain much more solid matter than the myce- 

 lium; the water content in two analyses of spores amounted to about 39 

 and 44 per cent respectively. Bacterial spores have not been analyzed, 

 but probably are much the same. 



Cell Wall. — The membrane of microorganisms does not generally 

 consist of true cellulose (C6Hio06)x, though it is found in some cases. 

 Other compounds, related to cellulose, are more common; chitin* 

 (C18H30N2O12), or another very similar nitrogenous compound is also 

 found. The slime surrounding some bacteria, and the capsules, 

 consist largely of carbohydrates, but often contain some protein. 



* Chitin when hydrolized yields glucosamine and acetic acid. 



CisHaoNaOii + 4H20 - aCHaOHCHOH-CHOHCHOHCHNHj-CHO + aCHs'COOH. 



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