GENERAL BACTERIAL METABOLISM 69 



The amount of material required for the catabolic (vegetative or 

 fuel) phase of the bacterial cell, on the contrary, is relatively large. 

 The energy requirement of cellular organisms varies rather with the 

 area of their surface than according to their actual volume; conse- 

 quently, very minute organisms, as bacteria, in which the surface is 

 relatively very great in comparison with their size, would require much 

 more material for energy purposes than for structural purposes. For 

 example, the total surface area of a million average-sized cocci (each 

 1 micron in diameter) would be approximately 3.1416 sq. mm.; the 

 weight of these organisms, assuming the specific gravity to be 1.030 

 (which is reasonably accurate), would be about 0.00054 mg. The 

 combined surface of all the cocci in an actively growing broth culture 

 of such organisms would be very considerable. It must be remembered, 

 however, that these figures do not carry any specific basis for the 

 measurement of bacterial activity in terms of chemical or physical 

 phenomena; they merely express in a very general manner the physical 

 basis for the apparent disproportion observed between the size of 

 bacteria and the amount of change they induce in their environment. 



The energy phase commences theoretically when the cell is morpho- 

 logically complete, and' it is a continuous process which ends only with 

 the death of the cell. It may be reduced to a minimum when the cell 

 enters upon a latent state of existence, as in spore formation; it is 

 greatest when the organism is growing in a favorable medium at the 

 optimum temperature, and it is restricted proportionately when 

 environmental conditions become unfavorable. 



The life-history of a culture in which innumerable bacteria are 

 growing can not be sharply divided into the anabolic and catabolic 

 phases. During the first few hours after inoculation, however, the 

 anabolic aspect predominates; later the catabolic aspect predominates. 

 Thus, colon bacilli inoculated into dextrose broth fermentation tubes 

 do not produce gas in visible amounts during the first few hours of 

 incubation, although the medium gradually becomes turbid, due to the 

 rapid multiplication of bacteria. Somewhat later gas formation is 

 observed, and it then proceeds with considerable rapidity. The 

 production of gas is indicative of a period of great vegetative activity 

 in which large numbers of mature colon bacilli utilize the dextrose for 

 their energy requirements. Still later the production of gas ceases, 

 the activities of the organisms diminish, and the culture finally dies 

 out as waste products accumulate in sufficient amounts. 



Those bacteria habitually pathogenic for man induce less striking 

 physical and chemical changes in their environment, as a rule, than 



