22 BACTERIOLOGY FOR NURSES 



sible for the spread of disease their immediate disinfection is 

 imperative. 



RESULTS OF BACTERIAL GROWTH 



Not only are bacteria influenced by their surroundings, but they 

 in turn exert a tremendous influence on these surroundings. The 

 effects of bacterial growth depend largely on the species and on the 

 composition of the substance on which they happen to be growing. 



Light. Twenty different species of bacteria have been de- 

 scribed which have the power of emitting light. The phosphor- 

 escence sometimes seen on decaying meat and fish is due to the 

 growth of these organisms. They are widely distributed in nature 

 and grow most luxuriantly in media rich in salt, as in sea-water. 

 It is supposed that the phenomenon is caused by a substance, 

 photogen, which is closely combined with the cell substance. 



Heat. The elevation of temperature in substances undergoing 

 bacterial decomposition, such as tobacco, manure, etc., is often 

 attributed to bacteria. It is more generally supposed that the 

 heat is due to chemical reactions. 



Pigment. When bacteria growing on culture media have 

 become sufficiently numerous to be seen with the naked eye, they 

 appear as a more or less moist grayish mass. Certain species, 

 however, have the ability to produce a pigment which may give 

 to this mass a brilliant hue. According to the species the color 

 may be violet, blue, red, green, orange, or yellow. The nature of 

 the pigments or the purpose they serve are not fully understood ; 

 they are generally thought to be related to the lipochromes, the 

 coloring matter met with in the yolk of eggs, carrots, etc. 



Chemical Effect. As bacteria consume the material which 

 serves them as food they break up the complex organic molecules 

 into simpler ones and thus entirely change the chemical nature of 

 their surroundings. Three different forms of bacterial activity 

 may occur : 



1. The nourishment of the cell protoplasm itself. 



2. Excretion from the bacterial cell of waste products. 



3. Production of secretions of the nature of ferments or enzymes, which 



disintegrate the food substance on which they are growing. 



