52 COLOUR IN NATURE chap. 



coloured Bacterium found in stagnant river -water, 

 in which the peculiar pigment was confined to the 

 protoplasm of the individuals and did not extend 

 into the jelly surrounding the colonies. Mr. Slater 

 has similarly described a form producing a bright 

 red pigment which is confined to the cells. On the 

 other hand, in the case of Micrococcus prodigiosus, 

 the red pigment is confined to the masses of 

 mucilage surrounding the colonies and does not 

 occur within the cells at all, while in yet other cases 

 the pigment may be found only in the substance in 

 which the colonies are living. 



As to the conditions under which the pigments 

 are produced, it is well known that Micrococcus pro- 

 digiosus loses its power of producing pigment at high 

 temperatures, while light is necessary for the produc- 

 tion of the purple pigment of Beggiatoa roscopersicina. 

 This pigment is of especial interest because, according 

 to Engelmann (1888), its presence in the organism is 

 associated with the power of breaking up carbonic 

 acid and setting free oxygen, therefore it has a 

 function equivalent to that of the chlorophyll of 

 green plants. In the case of Bacillus pyocyaneus, 

 according to Gerrard, the power of pigment produc- 

 tion is dependent upon the nature of the medium, as 

 well as upon the particular race of the microbe. 



As a point of interest with regard to the chemical 

 nature of the pigments, we may notice that in 1889 

 Zopf described a yellow pigment formed by Bacterium 

 egregium as a lipochrome, and stated that this was the 

 first time that lipochromes had been described as 

 products of bacterial action ; he has since described 

 other cases. The bright red Micrococcus pigment is 



