108 BACTERIOLOGY. 



In harmony also with the above facts, is the 

 discovery of Engelmann that other pigments 

 besides leaf-green are found among the lower 

 plants, and that these pigments are, like chlo- 

 rophyl, qualified by their physical power of 

 absorption to aid in the assimilation of car- 

 bonic acid. Such pigments are found among 

 diatoms and, according to Engelmann, the 

 bacterio-purpurin of Beggiatoa is a pigment 

 of this character. Chlorophyl, which has 

 already been found in one bacterial species, 

 the Bacterium chlorinum of Engelmann, was 

 merely the one pigment which by adaptation 

 and selection became favored quantitatively. 

 These facts, discovered by Pringsheim, Engel- 

 mann and Hueppe, and the views advanced 

 by these naturalists, have brought about a 

 fundamental broadening of the scope of plant 

 physiology. 



The fact that nitrifying bacteria are able 

 to utilize not only ammonium carbonate but 

 even such compounds as carbon dioxide and 

 ammonia was confirmed two years later by 

 the Russian investigator Winogradsky, and 

 supplemented in important particulars. He 

 was greatly mistaken in his conception of the 

 actual chemical process of synthesis, however, 

 since he thought that urea was formed first, 

 while, in reality, urea must be changed into 



