FOOD RELATIONSHIPS OF BACTERIA 63 
ti^•ely less water and consequently a greater proportion of proteins 
and ash. Analyses of the spores of Penicillium glauciim by Cramer^ 
show a distinctly greater amount of nitrogenous substance and of 
extractives, together with a surprisingly small amount of ash. Pos- 
sibly the low ash content explains in part the high resistance to heat. 
The analysis of dried spores follows (Penicillium glaucum spores) : 
Per cent. 
Protein 28.44 
Ether extract 7 . 30 
Alcohol extract 30.40 
Cellulose(?) 11.10 
Starch(?) 17.10 
Ash 1.90 
Reinke- has suggested that the sporoplasm is an anhydride of the 
cytoplasm of the vegetative cell. Sporulation implies that relatively 
considerable amounts of water must be taken up by the spore sub- 
stance in order to regain the proportion of this substance found in 
the parent organism. 
D. FOOD RELATIONSHIPS OF BACTERIA. 
1. General. — Food is any substance which a living organism may 
utilize, either by making it a part of its living material or as a source 
of energy. Food which is suitable for utilization by any organism 
must contain all the elements necessary for the building up and 
maintenance of that organism. Analyses of bacterial cells, which 
have been given in preceding tables, show them to be made up of 
the same elements as those of the higher plants and animals; viz., 
carbon, hydrogen, oxygen, nitrogen and phosphorus, together with 
smaller amounts of sodium, potassium, sulphur, calcium and mag- 
nesium. P'oods to be fully suitable for bacterial needs, therefore, 
should contain these elements. It should be stated, however, that the 
food requirements of bacteria vary within wide limits, but the above 
statements are generally applicable. 
2. Sources of Food, (a) Nitrogen.— The nature of the compounds 
in which nitrogen must be presented to bacteria as food varies greatly 
among the different groups. The nodule bacteria found in the nodules 
on the roots of many leguminous plants actually utilize atmospheric 
nitrogen: nitrifying bacteria found chiefly in the soil derive their 
nitrogen requirement chiefly from mineral salts which are oxidized 
through their activities to nitrites and eventually to nitrates. From 
this very simple source of nitrogen these bacteria are able to synthesize 
the complex nitrogen-containing proteins of their bodies. 
The majority of bacteria, including not only the saprophytic organ- 
isms but most of those pathogenic for man, animals and plants as well, 
1 Arch. f. Hyg., 1894, 20, 197. 
2 Quoted by Kruse: Allgem. Mikrobiol., p. 57. 
