CONDITIONS OF LIFE OF THE FISSION FUNGI. 533 



anaerobric growth of these bacteria to a marked degree. 

 In the case of some organisms, for example, bacillus 

 lactis aerogenes (Escherich), it has been demonstrated 

 that they can only exist without air when fermentescible 

 material is present, and fermentation is going on. 

 The fermentations set up by these organisms are ap- 

 parently not injuriously affected by the access of oxygen, 

 but on the contrary are favoured. 



In contrast to these groups we have a third, which is Obligatory 

 composed of " obligatory aerobes " ; these organisms can- aerobes - 

 not grow when air is excluded, even though they could 

 otherwise excite fermentation. Their growth is inter- 

 fered with by any marked diminution in the amount of 

 air, and under these circumstances one or other of their 

 functions may cease (for example, the production of 

 colouring materials, of ferments, &c.) ; on the other 

 hand, their life and growth is much favoured by artificial 

 increase in the tension of the oxygen. To this group 

 belong, for example, bacillus subtilis, bacillus ae'ro- 

 philus, &c. Nevertheless, within this group there are 

 marked differences as regards the quantity of oxygen 

 necessary, so that we can only lay down a general law, 

 viz., tbat each of these species of bacteria requires a de- 

 finite amount of oxygen. The fermentative action of the 

 bacteria belonging to the group of obligatory aerobes is 

 without exception favoured by the access of air ; for ex- 

 ample, the lactic, and more especially the acetic, fermen- 

 tation. According to Hoppe-Seyler,* a continued and 

 marked impregnation of the nutrient medium with air 

 has a favourable action on the development of many 

 putrefactive bacteria, as well as on the course of the 

 putrefactive fermentations set up by them, and hence 

 we may conclude that some of the bacteria which can 

 excite fermentation belong to the group of aerobes, while, 

 on the other hand, many obligatory aerobes also take 

 part in this process. 



We can say very little which is of general appli- concentration 

 cability as regards the most favourable proportions of of the nutrient 

 the individual nutrient materials, on account of the 



* Zeitschr.f. physiol Chem., vol. 8, p. 214. 



