CHAPTER I. 

 FOOD OF MICROORGANISMS. 



THE COMPOSITION OF THE CELL. 



For the study of the amounts and kinds of different food substances 

 used by microorganisms, it will be necessary to know first the material 

 that constitutes the cells. Naturally, the main constituent of the cell 

 is water. 



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 considered 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 organ- 

 isms grown in concentrated solutions as the organisms of salted meat 

 and the molds growing in strong sugar solutions contain more solids. 

 Spores of molds contain much more solid matter than the mycelium; 

 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 (C 6 H 10 O 5 ) X , though it is found in some cases. 

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

 (C 18 H 30 N 2 O 12 ), 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. 



CELL CONTENTS. The main portion of the cell is the protoplasm, a 

 mixture of protein substances, each of which has a very complex nature. 

 Enzymes which play an important role in metabolism (page 135) are 



* Chitin when hydrolized yields glucosamine and acetic acid. 



C 18 H 30 N 2 O 12 + 4H 2 O=2CH 2 OH-CHOH"CHOH-CHOH-CHNH- 2 CHO + 3CH' 3 



87 



