1890 THE MICROSCOPE. 137 



form of a compound, such as sugar or proteid, since they 

 have no (chlorophyll and are therefore unable to utilize 

 the carbon dioxide of the air as green plants do. Nitrogen 

 is derived from either organic or inorganic compounds, 

 such as proteids or ammonia, except one group (legume 

 bacteria) whicii is able to employ the nitrogen of the at- 

 mosphere. Moisture is essential, for while desiccated 

 bacteria retain their vitality for some time no growth 

 takes place except in the presence of moisture. As re- 

 gards temperature the range in wliich growth may take 

 place is very wide and the extremes which prove destruc- 

 tive are still much wider. The lowest point at which 

 growth takes place is about 45° F. and the highest about 

 110° F. , although within a few years there have been 

 isolated forms that grow only at a much higher tempera- 

 ture, 140° F. The most favorable temperature for or- 

 dinary forms is from 70°-100°F., the last being the re- 

 quirement of the disease-producing forms. 



If the temperature is congenial and moisture present 

 it is surprising how small an amount of organic matter 

 will support tliem. It has been found that certain forms 

 cannot only live but can multiply with great rapidity in 

 double distilled water where the only organic matter 

 present is in the particles of dust on the receptacles which 

 thorough washings failed to remove. 



The Wide Distribution of Bacteria. — The necessary 

 conditions of growth, solutions of organic nitrogenous 

 substances, are so widely distributed that bacteria are 

 found almost everywhere on the surface of the globe, 

 except in high altitudes, the air of mid-ocean, the deep 

 layers of the soil, and in the circulating fluids of the nor- 

 mal plants and animal body. 



Relation of Bacteria to Disease. — While many 

 scientists both before and after Van Leeuwenhoek's dis- 

 covery contended that bacteria were the cause of infectious 



