-9- 



is still, as a rule, too great. Hence, with a sterilized knife 

 a minute amount of material is taken from the surface of 

 potato No. 2 and transferred to that of potato No. 3, where 

 it is spread as before. 



If the inoculation is properly carried out the third 

 potato will have-but a few bn.cteria scattered over the sur- 

 face, and separated by inch or more. Each germ thus 

 isolated from its neighbor soon multiplies so that in 24 to 

 36 hours a small growth of about the size of a pin head 

 becomes visible. This isolated growth is known as a 

 colony, and inasmuch as it is derived from a single cell it 

 is &pure culture of that organism. 



In this and all subsequent work successful results and 

 freedom from danger depend upon the rigid sterilization 

 of all articles used. Hence, sterilize all instruments, 

 wires, etc., immediately before use, and immediately after 

 use, before placing them back on the table or in the 

 tumbler. 



LABORATORY WORK. Make dilution culture (on three 

 potatoes) of the Micrococcus prodigiosus. 



Mass culture (single potato) of Orange sarcine. 

 Red bacillus of water. 

 Violet bacillus of water. 



