92 BACTERIA. 



the oxygen and the nitrogen are severed, and the free oxygen is 

 immediately pounced upon by the carbon and the hydrogen, 

 which are set free from one another, each of these elements 

 taking up a certain quantity of the freed oxygen ; the 

 atoms of nitrogen having, of course, a strong affinity for one 

 another, combine, and a small portion of oxygen is set free. 

 The amount of energy released here is very great indeed, 

 and it is the more readily observed, and even measured, 

 from the fact that the process goes on rapidly and violently, 

 as it usually does where the resolution is that of a very 

 complex body, into extremely simple substances. Other 

 examples given by Bunge are the resolution of nitrogen 

 trichloride into its constituent elements by " contact with 

 various substances, such as phosphorus, phosphorus com- 

 pounds free from oxygen, selenium, arsenic, some resins 

 (other kinds being inert), non-volatile oils, &c. ; " and he 

 instances chlorate of potash, which splits up into chloride 

 of potash and oxygen at a certain temperature, and, in 

 the presence of binoxide of manganese, ferric oxide or 

 oxide of copper at a much lower temperature ; he says : 

 " The presence of this substance probably so modifies the 

 heat-wave, that the atoms of the chlorate of potash are more 

 easily thrown into responsive vibrations, and thus decom- 

 posed. In the same way peroxide of hydrogen decomposes 

 on being brought into contact with platinum, gold, silver, 

 binoxide of manganese, &c. In these cases it is called an 

 effect of contact, or a catalytic effect. We can form the 

 following hypothesis of the process which goes on here, as 

 in the cases above cited : The substance which acts ( cata- 

 lytically ' exercises an attraction on one of the atoms in the 

 unstable molecule. It does not necessarily always unite 

 with the atom, but the unstable arrangement of the atoms 

 in the molecule is invariably altered to a stable one." 



Now let us see what actually takes place when grape sugar, 

 of which we have already spoken, is being split up into 

 alcohol and carbonic acid. We have seen that there is a 

 rise of temperature quite distinct from any heat that is 

 applied to bring about the fermentation. It has been proved 

 that in some way or other the presence of the yeast-plant 

 has a very definite effect in starting a process of fermenta- 

 tion, and there are theories as to the role that this yeast- 

 plant plays in starting the fermentation. In the first place, 



