GREAT STEPS IN ORGANIC EVOLUTION 853 



gets its carbon from carbonic acid ; yet this in darkness, and so by 

 some other process than that of the green plant. 



Here we must not make too much of the distinction discovered 

 by Pasteur between aerobic and anaerobic fermentative organisms. 

 The former are dependent upon accessible free oxygen, like the 

 animal world, and ordinary plants as well, not even excepting the 

 leaf in active photosynthesis; but the latter are independent of free 

 oxygen, and even inhibited or killed by it, though wresting their 

 needed oxygen from such of its compounds as they can attack. For 

 this mode of life Pasteur found in various yeasts as well as in bacteria ; 

 and biochemists have recently made notable advances in explaining 

 the processes of oxidation and reduction in the tissue-life of higher 

 organisms, though these, of course, also as a whole continue 

 respiring in the ordinary way. (See Cell Oxidations.) Still, it is 

 among bacteria that we find this anaerobic process most frequently, 

 and then usually, though not invariably, as an essential condition 

 of life. 



The protean physiology of bacteria, beyond that of plants and 

 animals, is already illustrated in so many ways that we may well be 

 on the outlook for more of them. "Iron bacteria" have been 

 described, yet remain dubious; but there is no doubt of the "sulphur 

 bacteria" which utilise sulphuretted hydrogen, and accumulate 

 granules of sulphur, which are believed to be reserves, assimilable 

 as foodstuft. And among these sulphur bacteria, some have a purple 

 pigment which enables them to utilise light-energy, in analogy to 

 green plants, yet probably not closely so. There are other bacteria 

 which can grow in air, and on ordinary media like most others, yet 

 also utilise hydrogen directly; others can decompose marsh gas (CH^) 

 as grezn plants do CO2, and yet others which can even thus utilise 

 the carbon monoxide so deadly to higher organisms. Here, then, 

 within the so-called genus Bacillus, we have new fields undreamed by 

 the ordinary vegetable or animal physiologist, yet now opening 

 before the biochemist. The present point is thus confirmed; that 

 here we are in a life- world widely and deeply different from our 

 familiar ones, and expressing potentialities of physiological evolution 

 beyond these altogether. Their adaptivity to environment, as shown 

 by pathological and other research, is greatly beyond that of plants 

 and animals, so here is indication of their distinctness from both. 

 Furthermore, all this evolutionary potentiality and variety of 

 functioning is practically unaccompanied by distinguishable changes 

 in form; whereas in higher forms of life structure and function 

 advance together. 



Pass thus from these strangely varied ways of life, so often 

 physiologically distinct from our familiar ones of animals and 

 plants, with Protozoa and Protophytes of kindred life-processes, to 

 their morphological aspect, so strangely simple, and so little differen- 



