CHAPTER III 



BACTERIA 



Morphology. Bacteria are microscopic, unicellular organisms 

 which appear in three fundamental forms. The spherical forms are 

 known as cocci and may be single, in chains or in bunches. The indi- 

 viduals may be perfectly spherical, elliptical or lancet-shaped. The 

 individual pus coccus has a diameter of from 0.4 to 1 micron.* The 

 cylindrical forms are known as bacilli. Some have plane and others 

 convex or rounded ends. Bacilli differ greatly in length, the longest 

 pathogenic bacillus, that of malignant edema, being 9 microns, and 

 the shortest, that of influenza, being 0.5 of a micron. Growth is in 

 the direction of the long axis and multiplication by transverse fission. 

 The shape of the spirilla is sufficiently indicated by the name. Involu- 

 tion forms will not be discussed. 



Spore Formation. The only spore-forming pathogenic bacteria 

 are those of anthrax, symptomatic anthrax, tetanus and malignant 

 edema. The spores are of endogenous origin, are highly refractive to 

 light, and resistant to heat, and chemical disinfectants. No bacillus is 

 known to form more than two spores and this is practically confined 

 to saprophytic organisms. The appearance of two spores in an anthrax 

 bacillus is rarely seen. The purpose of spore formation is not mul- 

 tiplication but preservation; it is a resting stage. Spore formation is 

 a result of the concentration of the nuclear substance. The spore may 

 be formed in any part of the cell, but the location in the same species 

 is usually constant. In some bacteria the spore does not exceed the 

 diameter of the cell; in others it is larger. A large spore located at 

 one end of a bacillus gives it a "drum-stick" appearance ; when in the 

 middle, it forms a "spindle-shaped" organism. Untoward conditions, 

 such as scarcity of food, the presence of deleterious agents and an 

 accumulation of metabolic products, favor the development of spores. 



* A micron is one thousandth of a millimeter and is the equivalent of 1/25,400 

 of an inch. 



