454 REPORT — 1893. 



evolution of gases (CO2, H, &c.) have gradually become modified so as 

 to endure for longer and longer periods of time the exclusion of oxygen ; 

 and finally some forms have become so far modified as to only find the 

 means of livelihood in the entire absence of oxygen, or, in other v/ords, 

 they have become obligatorily anaerobic. 



Thus, whilst Pasteur ascribes fermentation to the life of micro-organ- 

 isms in the absence of oxygen, it appears to me that the life of micro- 

 oi'ganisms in the absence of oxygen is necessitated by their power of 

 bringing about fermentative changes which banish oxygen from the 

 medium ; in fact, the fermentative capacity is probably antecedent to the 

 anaerobic capacity. 



Direct experiments as to how far aei'obic micro-organisms can be 

 trained to thrive in the absence of oxygen, and vice versa, are urgently 

 wanted ; but there is already sufficient evidence that fermentative capacity 

 is not dependent on absence of oxygen. I have already referred to this sub- 

 ject in connection with yeast fermentation, but it is equally true of bacterial 

 fermentations also; thus my Bacilhis ethaceticus ferments most vigorously 

 in the presence of air, but it would, of course, not be a fermenting organ- 

 ism in the commonly accepted sense of the word if it could not also 

 ferment in the absence of air, because in ordinary fermentations, as there 

 is no provision made for the continuous supply of air, if the organism 

 were obligatorily aerobic, the fermentation would at once cease as soon 

 as the oxygen initially present was used up. 



These views are moreover in entire harmony with the observations of 

 other investigators concerning fermentation bacteria. Thus amongst the 

 most obligatorily anaerobic organisms with which we are acquainted is 

 the common butyric ferment, the so-called Bacillus amylohacter, which 

 can only be cultivated in the entire absence of oxygen. It must not,^ 

 however, be imagined that the butyric fermentation is dependent upon 

 the absence of oxygen, for Hueppe has isolated and described a bacillus 

 which, whilst bringing about the same butyric fermentations as the B. 

 amylobacter, is aerobic. Of the primitive bacteria possessing the power 

 of exciting butyric fermentation we must conclude, therefore, that the 

 ancestors of the B. amylobacter became so far modified by long-continued 

 residence amidst anaiirobic surroundings as to have apparently lost the 

 power of aerobic growth altogether, whilst the ancestors of Hueppe's 

 butyric bacillus, having undergone less specialisation, can still flourish 

 either in the presence or absence of air. 



These instances which I have selected are only a few out of a large 

 number of similar cases which are recorded in literature, but they are 

 sufficient surely for anyone whose mind is not burdened and biassed by 

 preconceived ideas concerning species to draw their conclusions as to the 

 mutability of bacteria, whilst they show the rare opportunities which are 

 afforded by these micro-organisms for experimentally studying some of 

 the phenomena of evolution. 



Sanitary Aspects of Bacteriology. — The advances in bacteriology which 

 have probably excited most general interest are those which have refer- 

 ence to the maintenance of the public health ; the bacteriology of air, 

 water, soil, and articles of diet, disinfection, and the like. It would be 

 impossible for me in the time which is available to present to you even 

 the merest outline sketch of the enormous amount of work which has 

 been done during recent years in this department. I will confine myself 

 to a few points which appear to me to be of more particular interest to 



