THE PRODUCTS OF THE TISSUE CHANGE. 561 



&c.), as well as of their amide compounds, occurs very 

 often. We find one or other, or it may be a mixture of 

 them, in most of the cultivations of fission fungi even 

 when there has been no fermentation, but merely simple 

 consumption of the nutrient material and the multipli- 

 cation of the fungi ; they are present, however, in much 

 larger quantities when fermentation has occurred. 



More seldom, but perhaps also equally widely distri- Aromatic 

 buted, we find aromatic bodies (phenol, paracresol, &c.) prod 

 AS products of the tissue change of the fission fungi ; 

 these have as yet been found chiefly or only in ferment- 

 ing and putrefying mixtures. 



Further, numerous fission fungi produce ferments, ptomaine?, 

 others produce substances which act like poisons and erments - 

 resemble alkaloids, and are commonly grouped together 

 under the term ptomaines. These two products of 

 tissue change require, on account of their special im- 

 portance in hygiene, a special discussion in the follow- 

 ing pages. 



Colouring materials are in some cases very common, Colouring 

 in others they are among the rarer products of the m 

 tissue change. Red pigment is, for example, formed by 

 the pink yeast, by micrococcus cinnabareus, by bacillus 

 prodigiosus, by bacillus indicus ; green colouring matter 

 by bacillus pyocyaneus, bacillus fluorescens putidus, 

 bacillus erythrosporus, bacillus fluorescens liquefac., 

 &c. ; blue colouring matter by bacillus cyanogenus, and 

 in putrefying mixtures (Brieger, Rohmann) ; violet by 

 bacillus janthinus ; brown by bacillus fuscus ; yellow by 

 very numerous micrococci and bacilli. These pigments 

 are very rarely present in the cells or in the cell walls, 

 (these are usually colourless), and it is only the sub- 

 stratum on which the fungi grow that is impregnated 

 with the pigment. It has been further observed, 

 and has recently been ascertained by Liborius in the 

 case of a large number of pigment bacteria, that the 

 colouring matters are only formed when free access 

 of air is allowed, while if the access of air is even only 

 moderately hindered (by covering with oil, &c.), the sub- 

 strata and the colonies remain completely colourless, 



36 



