214 METABOLISM 



gain in energy in these other cases also. We must extend our original definition 

 and say that fermentation is dissimilation which is not carried, as in respiratory 

 combustion, to the final stages. Under these circumstances we must also 

 regard the formation of organic acids in succulents as a case of fermentation. 

 Attempts to bring other fermentative actions within the scope of our 

 observations land us in a region where the data are most contradictory — more 

 indeed than need be. Up to the time of Pasteur's first important investiga- 

 tions we knew nothing of what is nowadays known as a 'pure culture'; before 

 that, investigators experimented with cultures usually containing several 

 organisms and they were consequently unable to determine what part each 

 played in the production of the final result; and nowadays, when the need for 

 pure cultures has become generally recognized, the effort to achieve practical 

 results in the physiology of fermentation has increased to such an extent that 

 important scientific questions requiring solution have been quite ignored. Hence 

 there has arisen a mass of literature which can only be surveyed by specialists. 

 Under these conditions it is to-day more than ever difficult to give an outline of 

 the present position of our knowledge of this subject. [Lafar has performed 

 an extremely valuable service in giving in his Handbook of Technological 

 Mycology (Jena, 1904, onwards) an exhaustive account of all the important 

 fermentative processes used in the Arts. This work, which is still in course of 

 publication, may be referred to for further details.] 



Alcoholic fermentation, that is to say the formation of ethyl-alcohol, is 



not confined to yeast ; it may be induced also, as we have seen, under certain 



' conditions by Mould-fungi as well as by higher plants, but 



®v %i^ °^^y ^y ^ relatively small number of Bacteria. It is true 



^ ^^ that certain Bacteria have the power of forming higher 



/^Q ^^ alcohols ; thus, for example, fusel oils (a mixture of 



V s?^^ propyl-, butyl-, and especially amyl-alcohols), which are 



^^i^^ developed during the manufacture of brandy, and par- 

 ^^ ^'^ ticularly of potato spirit, are due apparently to the action 



Fi 8 Bacillus but licus ^^ Bactcria ; pure yeasts give rise to none of the higher 

 Afte?BEijERiN"K"x 9^. '"'■^' alcohols. Beijerinck (1894) has carefully studied a 

 bactermm which induces the formation of propyl- and 

 butyl-alcohols, and to this form we may devote some little attention since it is in 

 many respects an interesting contrast to yeast. Bacillus hutylicus {Granulobacter 

 hutylicum^ Beij.) (Fig. 38), as it is named, is an elongated rod of considerable 

 size ; it contains a large amount of a carbohydrate, the so-called granulose, 

 colouredbluebyiodine,andfinallyformsendospores inmore or less spindle-shaped 

 swellings. In nature this bacterium occurs with great constancy on the fruits of 

 certain species of barley and consequently also in the meal formed from them. 

 If such meal be made into a mucilage by cooking for a short time, the spores, 

 which resist, at least for a few minutes, this high temperature, quickly begin to 

 germinate, and the organisms increase rapidly in number. At the same time the 

 starch is changed, by a diastatic enzyme excreted from the cells into maltose, 

 and this later on is in part used in constructing new organisms and in part is fer- 

 mented. The fermentation consists in the development of hydrogen and carbon- 

 dioxide in varying proportions, while butyl-alcohol is also developed. The net 

 amount of this characteristic product is not very great, amounting as it does only 

 to about 1-3 per cent, of the meal. According to more recent research propyl- 

 alcohol is also formed (Beijerinck, 1889 ; Archiv. neerland. II, 2, 402, note). 



Bacillus hutylicus — apart altogether from its specific zymatic capacities — 

 differs, however, from yeast in one noticeable point, namely, in its relation to 

 oxygen ; it is strongly anaerobic. In order to obtain butyl-alcoholic fermenta- 

 tion the greatest care must be taken to exclude oxygen from the nutritive sub- 

 stratum, since if sweetwort be used as the culture medium small quantities of 

 oxygen are found to be directly injurious. Beijerinck removed most of the 



