566 VITAL ACTIONS OF THE LOWER FUNGI. 



ditions of existence have again become normal. This 

 matter of attenuation is more fully entered into in the 

 following chapter on the conditions affecting the death 

 of the organisms. 



injury of the The products of the tissue change of many of the 



bacteria by fl . . 6 . , , . \ ., . 



the products nssion fungi appear to exercise a remarkable inhibitory 

 t/ssuTchange. act i n on tne growth and multiplication of the same 

 organisms. This has been definitely ascertained in the 

 case of certain fermentations; thus, as is well known, in 

 the alcoholic fermentation, alcohol when present in 

 the nutrient substratum in the proportion of 14 per 

 cent, interferes with the vital activity of the yeast 

 cells ; similarly, the ammoniacal fermentation of urine 

 ceases when the amount of carbonate of ammonium 

 in fermenting has risen to about 13 per cent.; in like manner the 

 lactic acid and the butyric acid, which are formed in 

 the corresponding fermentations, must be neutralised 

 by the addition of carbonate of lime or of oxide of zinc, 

 because otherwise the constantly increasing amount of 

 free acid is injurious to the life and the fermentative 

 activity of the bacilli which are at work (lactic acid is in- 

 In growths jurious even in the amount of 0*8 per cent.). Analogous 

 fermentation, actions have also been often suspected with regard to the 

 products of the tissue change of many bacteria where no 

 fermentation is going on, but in these instances it has 

 not been demonstrated with complete certainty. The 

 relatively rapid death of these bacteria in nutrient sub- 

 strata which still contain a large amount of good nutrient 

 materials is usually explained by the hurtful action of 

 the accumulated products of their own tissue change. 

 Suppositions have also been frequently made as to the 

 more precise nature of the materials which come into 

 play in this action ; attention has been chiefly paid to 

 the aromatic products (phenol, paracresol, &c.), which 

 are found in numerous putrefactive processes, for these 

 as a matter of fact exert an energetic inhibitory action 

 Nature of the even in very small quantities. But even for these views 

 products. proof is still wanting, because from the occurrence of 



