FOOD OP MICROORGANISMS 149 



Gell 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 r61e in metabolism (page 178) are 

 produced in the protoplasm and are either secreted or retained. All 

 products of metabolism will be found in the protoplasm of the cell in 

 small quantities. Among other substances frequently found in micro- 

 organisms may be mentioned glycogen (C6Hio06)„ which can be readily 

 detected by the brown color it gives when acted upon by iodine. Gly- 

 cogen may be considered as a reserve substance stored by the organism. 

 Another carbohydrate staining blue with iodine is stored by B. amylo- 

 hacter. Fat is commonly found in many bacteria. The amount of 

 fat in some bacteria is surprisingly high. In the tubercle bacterium 

 26.0 to 39.29 per cent of the total solids is fat. All acid-fast bacterial 

 cells have a very high fat content. Other bacteria also contain occa- 

 sionally as much as 8 per cent fat. Yeasts seem to have a lower fat 

 content, while in molds it has been found to vary from 0.5 10,50.5 per 

 cent. Many other products of organic nature are found occasionally, 

 but their importance is not determined. Protein is sometimes ac- 

 cumulated in certain places of the cell and gives a granular appearance 

 in the stained cell. Volutin may be such reserve protein. 



The minerals of the microbial cell are very essential, and hke the 

 organic materials, necessary for the life of the cell. The total ash of. 

 bacteria, yeasts, and molds, is small, about 1.5 per cent to 8 per cent of 

 the dry cell. The important minerals which seem necessary for the con- 

 struction of the cell are potassium, calcium, magnesium, iron, manga- 

 nese, and of the metalloids, nitrogen, phosphorus, and sulphur. 

 Some other minerals are usually found, but seemingly are unnecessary 

 to the cell, as sodium and sihcon. 



Amount of Food Required 



The amount of food that is ordinarily decomposed by microorgan- 

 isms and the amount that is absolutely necessary, differ widely. The 

 quantity of organic and inorganic matter just sufficient to support a 

 very weak growth is certainly very small, since a few species will 

 multiply to some extent in ordinary distilled water. Such water, after 

 having stood for some time, is found to contain several thousand 

 bacteria per c.c. It may seem to the layman that in such water it 



