114 BACTERIOLOGY. 



substances. As might be expected, the products will differ 

 according to the kind of organism at work, the temperature 

 and the amount of oxygen, etc. The bacterium termo of 

 the older writers, is to be considered as a group name 

 covering a number of saprogenic bacteria, rather than any 

 one individual organism. 



Pigment Production. 



The various bacteria which give rise to pigments are 

 said to be chromogenic. The activity of these organisms is 

 not limited to the production of pigment. Thus, the well- 

 known golden, pus-producing micrococcus not only produces 

 a pigment, but is also pathogenic, and may, indeed, induce 

 typical fermentations. It is evident that the pigment is to 

 be considered as one of the many chemical products elabor 

 ated by the bacterial cell. 



The number of chromogenic bacteria probably exceeds 

 one hundred. All shades of color may be found among the 

 different individuals of this group. It has been shown, here- 

 tofore, that the majority of bacteria are perfectly colorless. 

 In only a very small number of bacteria do the cells contain 

 a pigment. The contents of the cell, in such cases, may be 

 colored a light pink or purple, green, yellow or brown. In 

 the first case the pigment, known as bacterio-purpurin, 

 may be considered as allied to chlorophyll, inasmuch as the 

 organisms which contain it, unquestionably, give off oxygen 

 in the presence of light. The green pigment, present in a 

 few species may, in like manner, be possibly related to 

 chlorophyll. 



With the exception of the instances just mentioned, the 

 cells of the chromogenic bacteria are perfectly colorless. 

 It is clear that in these cases, the pigment, or its antece- 

 dent, is made within the cell, and is excreted or passed out 

 as rapidly as it is made. Moreover, there is reason to be- 



