680 CONSTANCY AND MUTABILITY OF FUNGI. 



suitable acclimatisation of bacteria the result will be 

 not a loss or diminution, but a multiplication of their 

 specific characters, and that the properties thus acquired 

 will again be lost after a few generations when the 

 abnormal external conditions are replaced by normal 

 ones. 



Niigeli's views Nageli, Buchner, Wernich, and others have formerly assumed 



as to the ^ e existence of a very rapid and limitless alteration of the 



mutability or , /. -i -i ,-,-, 



the bacteria, characters ot species of bacteria which had up to that time 



been distinguished from each other. " According to my view 

 each of the species of bacteria could occasion the formation 

 of lactic acid, putrefaction, and various forms of disease. 

 Each species has the power of accommodating itself to un- 

 equal external conditions, and consequently of appearing in 

 various forms morphologically and physiologically peculiar. 

 The adaptation or acclimatisation may be more or less com- 

 plete and more or less permanent, according to the time and 

 the other factors which are at work. . . . Thus forms of an 

 unequal degree of development and of unequal constancy- 

 would be produced in accordance with the various external 

 conditions. The same bacterium would at one time live in 

 milk and form lactic acid ; at another on meat and cause 

 putrefaction ; again in wine, and lead to the formation of a 

 gummy substance ; subsequently in the earth without setting- 

 up any fermentation ; and finally in the human body, and take 

 part in some form of disease. ... It would on a soil which 

 was equally disposed for various fermentations occasion those 

 changes which most correspond to the physiological stage at 

 which it has arrived by its previous mode of life. Bacteria 

 which frequently change their habitat would of course retain 

 an indefinite character, and be equally well disposed to 

 assume different forms and to excite different fermentations " 

 (Nageli*). 



Nageli and Buchner found an experimental support for 

 these views in the observation that bacteria which caused 

 milk to become sour lost this property in a saccharine solu- 

 tion of meat extract, and caused there an ammoniacal fermen- 

 tation, and it was only after a hundred or more generations 

 in milk that the property of forming acid slowly recurred. 



Hueppe, however, tested this question accurately, and was 

 unable to make out any such variability in the behaviour of 

 the lactic acid bacilli, but he showed that an ammoniacal 

 fermentation could be caused in the milk by butyric acid 

 bacilli, which, in the form of resistant spores, could readily 



* Niigeli die niederen Pibe, Miinchen, 1877, p. 22. 



