Production of Heritable Variations in Bacteria 89 



acid, corrosive sublimate, and other metallic salts. It was 

 not at all difficult to cause the organisms to lose color when 

 cultivated with these chemicals ; keeping them at a high 

 temperature had the same effect. But in most cases, as soon 

 as the organisms were returned to natural conditions the 

 normal production of color was resumed; the "acquired 

 character" was not inherited. Similarly transitory modi- 

 fications of the color in other directions were produced. 

 'Such results were reached with infinite pains in a great num- 

 ber of experiments, with this organism and with other 

 colored bacteria. 



But in cultures in which the nutritive medium contained 

 potassium bichromate, certain white colonies appeared which, 

 when transferred to media without the chemical, continued 

 to remain white, though there appeared also red spots amid 

 the white. A long series of selections was carried on, choos- 

 ing always the whitest parts of the colonies, but the tend- 

 ency to return partly to the red condition could not be 

 gotten rid of by selection. It was found that the longer the 

 organisms were cultivated with potassium bichromate, the 

 more firmly was the white established. When it first ap- 

 peared the white color disappeared again as soon as the 

 organisms were restored to normal surroundings ; later the 

 white became hereditary, though there was always a tendency 

 for some part of the colonies to produce the red color. 

 Some similar results were reached also with other chem- 

 icals. 



In these cases therefore we have a most interesting tran- 

 sitional condition. The hereditary character of the race 

 has been changed, for now the colonies are largely white 

 under the same conditions in which they were formerly 

 red. But they still show a tendency to return to the original 

 character. 



But with another substance, corrosive sublimate, a white 



