666 ARTHUR ISAAC KENDALL 



every fifteen minutes. The theoretical descendants of a single microbe 

 after four hours of unrestrained growth would number almost thirty-three 

 thousand. Their combined volumes would be approximately 0.000066 

 cubic millimeter, 4 but their united surface areas would be nearly 0.33 

 square millimeter. It is obvious that the amount of structural substance 

 essential for the thirty-three thousand cholera vibrios would be little in- 

 deed; the quantity of material necessary to provide the requisite energy 

 for these organisms is relatively very large. 



The rapidity of reproduction among bacteria, therefore, furnishes an 

 additional explanation of the magnitude of transformation of nutritive 

 material, which is such a conspicuous feature of bacterial growth. From 

 this viewpoint, the activities of bacteria appear to lie within the realm of 

 colloidal chemistry the chemistry of surface relations. 



The relations between surface and volume of bacterial cells as an 

 explanation of the magnitude of bacterial metabolism cannot be empha- 

 sized to the exclusion of the specific activities of individual species or 

 types of bacteria, however. Bacillus proteus and Bacillus typhosus, for 

 example, are of nearly equal dimensions and multiply at nearly the same 

 rate. Nevertheless, the former is far more energetic, under apparently 

 parallel conditions, in its chemical transformations to obtain the elements 

 requisite for energy than the latter. 5 The fact remains, however, that in 

 general, bacteria effect changes in their chemical environment, both in 

 time and amount, greatly exceeding that to be expected from such minute 

 organisms, and the significant aspect of this activity is that associated with 

 the energy phase rather than the structural phase of their metabolism. 



2. The Influence of Saprophytism, Parasitism, and 

 Pathogenism upon Bacterial Metabolism 



From the viewpoint of mankind, bacteria may be classed for con- 

 venience as of three principal groups (Smith, Kendall (a)) : First, sapro- 

 phytic bacteria, living upon dead organic material, and usually without 

 significance in a pathogenic way. Their function in Nature is to bring 

 about deep-seated changes in dead organic matter, returning the essential 

 elements, as nitrogen, to the vegetable kingdom as fully mineralized com- 

 pounds ready for resynthesis into proteins and other necessary organic 

 compounds, by chlorophyll-bearing plants. Secondly, parasitic bacteria, 

 which live upon the body of the host* or in channels or cavities in free 

 communication with the exterior of the body of the host. Usually such 

 organisms are endowed with the power of multiplying within the tissues, 



*The cholera vibrio is approximately equal in size to the typhoid bacillus. 

 5 In general, it may be stated that non-pathogenic bacteria are more active 

 chemically than pathogenic bacteria. 



