GENERAL MORPHOLOGY AND PHYSIOLOGY OF BACTERIA. 31 



found in decaying vegetable matters, whereas psychrophile species are found 

 in cold water and cold soils. 



Bacterial life processes result in the formation of many substances, some 

 of which are of the greatest importance. It is impossible to estimate prop- 

 erly the enormous tasks performed by these minute organisms, nor shall we 

 at this time make any attempt to set forth the great good and the apparent 

 great harm done by them. We need only state that without rotting microbes 

 soil formation would be impossible, and without soil, higher plant and animal 

 life, as we now know them, would be impossible. Without plant food 

 digesting microbes crop growing would be impossible. The saltpeter depos- 

 its in South America and the iron deposits of the Mesabi range of Minnesota 

 are said to be the result of bacterial action. We make extensive practical 

 use of microbes in medical practice, in the dairying industry, etc. 



We will mention ohly a few substances of undoubted microbic origin. 

 Ptomaines and toxalbumins are well-known poisons elaborated by sapro- 

 phytic microbes which feed on meats and other organic substances, causing 

 the familiar putrefactive changes. Pathogenic microbes elaborate toxins 

 to which are due the manifestations of the disease. Acetic acid, lactic acid, 

 and butyric acid are elaborated by Bacillus aceticus, B. acidi lactici, and 

 B. butyricus, respectively. Some species liberate odoriferous substances, 

 others gases, coloring substances, phosphorescence, etc. The phosphor- 

 escence observed on the ocean is supposed to be due to bacteria (Bacillus 

 phosphorescent indicus). Phosphorescent bacteria occur in dead fish and 

 in meat. Old cultures in animal nutrient media and in the presence of 

 sodium salts are phosphorescent in the dark, sufficiently so, to have sug- 

 gested making bacterial lamps and signal lights: 



It has been suggested that certain diseases, of which the causes are at 

 present unknown (as yellow fever, measles, whooping cough), may be due 

 to organisms so small as to be invisible (ultra micro-organisms). It is known 

 that the virus of yellow fever will pass through the most compact clay or por- 

 celain filter. Attempts have been made to demonstrate the presence of 

 ultra micro-organisms by special photomicrographic methods, aided by 

 special illuminating devices (the ultra microscope of Siedentopf and 

 Szigmondy) but without success. Furthermore, no one has succeeded in 

 culturing such theoretically surmised organisms in artificial media, which 

 would certainly render them visible en masse. It may, however, be possible 

 that some ultra-organisms are obligative parasites hence will not develop in 

 artificial media. 



The biological (symbiotic) relationship of different species of bacteria to 

 each other and to their host are, in many instances at least, not well under- 

 stood. For example, it is not clear what biological relationship the different 

 species of bacteria in a mixed infection bear to each other. In the case of the 



