100 THE FERMENTS. 



added, so as to bring about the death of the cells proper. If some 

 of this liquid is now added to a solution of cane-sugar, an inversion 

 takes place, as before, but subsequent fermentation does not occur. 

 In the first experiment we thus see manifested the activity of the 

 living cell as such, as also that of its ferment ; while in the second 

 test only that of the ferment is shown. 1 



For the maintenance of life, in the case of the higher plants at 

 least, the organized ferments are of prime importance ; for, as has 

 been seen, it is through these low forms of life that the higher plants 

 are furnished their nitrogen in a form which they can subsequently 

 utilize. In their absence from the soil, vegetable life, such as we see 

 it, could probably not exist. In the gastro-intestinal tract of all 

 animals which have been examined in this direction innumerable 

 bacteria are also found, and it was long thought that their presence 

 here served a very definite purpose, and that animal life could not 

 go on in their absence. This view, however, has proved erroneous, 

 as Nuttall and Thierfelder conclusively demonstrated. They showed 

 that when a young guinea-pig, for example, is removed from the 

 mother animal by CaBsarean section under strict aseptic precautions, 

 and is subsequently fed with sterile food and is furnished with sterile 

 air, it will grow as well as a control-animal. While the presence of 

 bacteria in the animal body is therefore not essential for the main- 

 tenance of life, and while it is very questionable, indeed, whether 

 their presence in the alimentary canal serves any useful purpose at 

 all, we know, on the contrary, that the introduction of certain forms 

 is directly harmful, and that some of the normal inhabitants of the 

 intestinal canal may under certain conditions develop distinct patho- 

 genic properties. 



From a physiological standpoint the organized ferments are con- 

 sequently of secondary interest only in animal chemistry, while 

 pathologically they may be most important. It is thus known that 

 during their metabolism they can give rise to the formation of sub- 

 stances which are more or less toxic, and which when absorbed into 

 the blood cause definite pathological symptoms. Such bodies are the 

 so-called ptomains and toxalbumins. The former are basic sub- 

 stances which belong to the fatty series, and consist of carbon, 

 hydrogen, and nitrogen, and in some instances also of oxygen 

 (see page 91). 



While some of the ptomains are apparently harmless, others are 

 exceedingly poisonous, and these last are accordingly spoken of as 

 toxins. Representatives of the former group are cadaverin and 

 putrescin, two diamins, which are respectively pentamethylerie and 

 tetramethylene diamin, while typhotoxin and tetanin belong to the 

 latter class. The toxalbumins, on the other hand, are, as the term 

 indicates, albuminous substances, which in part at least belong to 



1 Buchner, it is true, has of late claimed to have succeeded in causing complete 

 fermentation also in the absence of the living cell, but his results, while confirmed 

 by some, are not IM yet accepted by al 1 . 



