PRODUCTS OF METABOLISM 1 77 



The chemical nature of microbial pigments is little known. They 

 are distinguished according to the solubility in various Uquids, water, 

 alcohol, ether, chloroform, benzol, and other solvents, and according 

 to the change of color caused by acid and alkali. A group of 

 carotin bodies, named because of their similarity to the pigment 

 of carrots, the prodigiosin bodies, named after B. prodigiosus, the 



Fig. ioi. — Bacteriopurpin, from a Rhodes pirillum, crystallized from a chloroform 

 solution. {After Molisch.) 



fluorescent pigments and perhaps a few other groups are distinguished, 

 but their chemical nature is rather vague as yet. The absorption of 

 distinct hues of the spectrum by solutions of these pigments is claimed 

 to be a very reliable means of distinguishing the pigments of different 

 species. 



Aromatic substances constitute another group of metabolic prod- 

 ucts. The chemical analysis accomphshes more with these com- 

 pounds than with pigments, since they are frequently well-known 

 compounds. The main difficulty arising in their identification is in 

 the very minute quantities of the products available. Some substances 

 with strong, mostly very disagreeable odors have already been men- 

 tioned: indol, skatol, hydrogen sulphide, mercaptan, the amins and 

 ammonia, butyric acid, and some of the higher alcohols. There re- 

 main to be mentioned certain oils and esters giving rise largely to 

 pleasant aromas. The formation of aromatic oils has been established 

 although their nature is entirely unknown. The same is true with the 

 esters. The substance causing the fishy flavor in butter is volatile 

 with steam and is neither of an alkaUne nor acid nature. The strong 

 odor of freshly plowed earth is caused by an Actinomyces; the odor 



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