Conditions Prejudicial to Growth of Bacteria 41 



bacillus in a mixture containing ammonium carbonate 

 0.35 per cent., potassium phosphate 0.15 per cent., 

 magnesium sulphate 0.25 per cent., and glycerin 1.5 

 per cent. Some of the water microbes can live in dis- 

 tilled water to which the smallest amount of organic 

 matter has been added; others require so concentrated 

 a medium that only blood-serum can be used for their 

 cultivation. The statement that certain forms of bac- 

 teria can flourish in clean distilled water seems to be 

 untrue, as in this medium the organisms soon die and 

 disintegrate. If, however, in making the transfer, a drop 

 of culture material is carried into the water with the bac- 

 teria, the distilled water ceases to be such, and becomes a 

 dilute bouillon fitted to support bacterial life for a time. 

 Sometimes a species with a preference for a particular 

 culture medium can gradually be accustomed to another, 

 though immediate transplantation causes the death of the 

 organism. Sometimes the addition of such substances 

 as glucose and glycerin has a peculiarly favorable influ- 

 ence, the latter, for example, enabling the tubercle bacillus 

 to grow upon agar-agar. 



Moisture. A certain amount of water is indispensable 

 to the growth of bacteria. The amount can be exceedingly 

 small, however, Bacillus prodigiosus being able to develop 

 successfully upon crackers and dried bread. Artificial 

 culture media should not be too concentrated; at least 

 80 per cent, of water should be present. 



Reaction. Should the pabulum supplied to bacteria 

 contain an excess of either alkali or acid, the growth of the 

 organisms is inhibited. Most true bacteria grow best in a 

 neutral or feebly alkaline medium. There are exceptions 

 to this rule, however, for Bacillus butyricus and Sarcina 

 ventriculi can grow well in strong acids, and Micrococcus 

 urea can tolerate excessive alkalinity. Acid media are 

 excellent for the cultivation of molds. 



CONDITIONS PREJUDICIAL TO THE GROWTH OF 

 BACTERIA. 



Light. Most bacteria are not influenced by the presence 

 or absence of ordinary diffused daylight. The direct 

 rays of the sun, and to a less degree the rays of the electric 

 arc-light, retard and in numerous instances kill bacteria. In 



