108 RESPIRATION 



skin of, say, the grape : rupture of the skin of the fruit provides 

 a nutrient medium eminently suitable for growth and repro- 

 duction accompanied by a free access of oxygen. A period 

 of intense activity immediately supervenes and budding takes 

 place, under the continued action of the oxygen, with remark- 

 able rapidity : this activity necessitates a continuous supply 

 of energy, which is provided by fermentation. Reproduction 

 and fermentation thus are correlated. " That we can by 

 means more or less artificial keep the reproductive power of 

 a yeast in abeyance, whilst still availing ourselves of its fer- 

 mentative power, has hitherto obscured the relation of the 

 two functions, and hence has given rise to the somewhat 

 exaggerated idea of the purposeless and prodigal waste of the 

 yeast cell regarded as a living unit." 



In view of the definition given above, it is obvious that 

 any process, oxidative or reductive, which liberates energy 

 available for use by the plant is to be included amongst res- 

 piratory processes, irrespective of the initial products con- 

 sumed and the final products evolved. Thus, in addition to 

 the oxidative processes of the higher plants in which fats, 

 carbohydrates, proteins, and, in extreme circumstances, even 

 protoplasm may be physiologically consumed, the diverse meta- 

 bolic processes of bacteria and comparable organisms in reduc- 

 ing sugar to alcohol, sulphate to sulphide, or oxidizing alcohol to 

 acetic acid, lactose to lactic acid, ammonium salts to nitrites, 

 nitrites to nitrates, and so on, are all processes of respiration, 

 notwithstanding the fact that many of these activities may 

 be extra-cellular. For green plants, oxygen is a common 

 essential, although, as is well known, certain organisms, such 

 as the lactic bacteria, can only flourish in the absence of oxygen, 

 whilst others, although oxygen is essential normally, have the 

 faculty of tiding over a period of its absence. Hence respi- 

 ration may be distinguished as aerobic, anaerobic,* and facul- 

 tative anaerobic. The final waste products are diverse and 

 depend upon the chemical nature of the material consumed 



* The use of the term, " intra-molecular respiration" for anaerobic 

 respiration is wrong since all foims of respiration are essentially intra- 

 molecular. 



