EVOLUTION OF BACTERIA 8i 



The size of bacteria is in inverse ratio to their importance 

 in the primordial and present history of the earth. The largest 

 known are slightly above i /20 of a millimetre in length and 

 1/200 of a millimetre in width. ^ The smaller forms range 

 from I /2000 of a millimetre to organisms on the very limit of 

 microscopic vision, i /5000 of a millimetre in size, and to the 

 bacteria beyond the limits of microscopic vision, the existence 

 of which is inferred in certain diseases. The chemical consti- 

 tution of these microscopic and ultramicroscopic forms is 

 doubtless highly complex. The number of these organisms is 

 inconceivable. In the daily excretion of a normal adult human 

 being it is estimated that there are from 128,000,000,000 to 

 33,000,000,000,000 bacteria, which would weigh approximately 

 5 5/10 grams when dried, and that the nitrogen in this dried 

 mass would be about 0.6 gram, constituting nearly one-half 

 the total intestinal nitrogen.- 



The discovery of the chemical life of the lowliest bacteria 

 marks an advance toward the solution of the problem of the 

 origin of life as important as that attending the long-prior dis- 

 covery of the chemical action of chlorophyll in plants. 



In their power of finding energy or food in a lifeless world 

 the bacteria known as prototrophic, or "primitive feeders," are 

 not only the simplest known organisms, but it is probable 

 that they represent the survival of a primordial stage of life 

 chemistry. These bacteria derive both their energy and their 

 nutrition directly from inorganic chemical compounds: such 

 types were thus capable of living and flourishing on the lifeless 

 earth even before the advent of continuous sunshine and long 



^ The influenza bacillus, s/io X 2/10 of a micron (i/iooo mm.) in size, and the germ 

 of infantile paralysis, measuring 2/ 10 of a micron, are on the limit of microscopic vision. 

 Beyond these are the ultramicroscopic bacteria, beyond the range of vision, some of 

 which can pass through a porcelain filter. See Jordan, Edwin O., 1908, pp. 52, 53. 



- Kendall, A.. I., 1915, p. 209. 



