CHAPTEE IV. 



BIOLOGY OF BACTERIA. 



IN the previous chapter the morphology of bacteria has been con- 

 sidered. It is, however, impossible strictly to separate the mor- 

 phology from the biology of these organisms. Involution forms and 

 spores are certainly morphologic features of bacteria, yet they cannot 

 be referred to without going to some extent into the biology of the 

 fission fungi. The present chapter will be more particularly devoted 

 to some important features in the life history of bacteria, as they 

 are dependent upon varying conditions of their existence with refer- 

 ence to environments, nutrition, metabolism, etc. It has previously 

 been stated that bacteria are as a class ubiquitous, that is, they are 

 found everywhere on or near the surface of our globe, in soil, water, 

 air, or the external surface of the bodies of plants and animals, and 

 in the intestinal tract of the latter. They are not found in the blood 

 or interior of tissues of healthy animals, nor to any extent in the 

 highest altitudes and latitudes. 



Temperature Limits. A most remarkable feature of bacterial life 

 in general is that they as a class can exist and multiply under a wider 

 range of temperature than any other class of organisms. There are 

 bacteria that multiply in sea water at C. (32 F.) and others 

 that multiply in springs at 75 C. (167 F.). Many individual species 

 exist and multiply under a wide range of temperature, but some, 

 particularly the pathogenic strict parasites of warm-blooded animals, 

 are quite limited in the latitude of temperature under which they 

 can exist and grow. Bacteria, as a rule, flourish and multiply most 

 rapidly at a definite temperature called their optimum temperature. 

 Beyond certain limits above and below the optimum temperature 

 they will not grow at all; these limits are called the maximum and 

 minimum temperature of their growth. The bacillus of mam- 

 malian tuberculosis has its optimum temperature at 37 to 38 C., 

 that of avian tuberculosis at 38 to 43 C.; the former its minimum 

 temperature at 29 C., the latter at 35 C.; while their maximum 

 temperatures are 41 C. and 46 C., respectively. These are examples 

 of strictly parasitic bacilli which have a very narrow range of tem- 

 perature at which they can grow and multiply. This is also true of 

 the strict saprophytes. On the other hand, facultative parasites, which 

 occur also as saprophytes, often have the wide range of 25 C. from 

 15 to 40 C., and more. 



Thermophile Microorganisms. Bacteria which multiply best at 

 very high temperatures (75 C.) are called thermophile, which, literally 



