FORMS OF RESPIRATION 71 



remarkable rapidity : this activity necessitates a continuous 

 supply of energy, which is provided by fermentation. Repro- 

 duction 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 fermenta- 

 tive power, has hitherto obscured the relation of the two 

 functions, and hence has given rise to the somewhat exagger- 

 ated 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 

 respiratory 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 protoplasm may be physiologic- 

 ally consumed, the diverse metabolic processes of bacteria and 

 comparable organisms in reducing 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 respiration may be distinguished as 

 aerobic, anaerobic,* and facultative anaerobic. The final waste 

 products are diverse and depend upon the chemical nature of 

 the material consumed and the method of its physiological 

 combustion, whether by aerobic or anaerobic means. 



The ordinary green plant, and certain non-green plants, 

 in their respiration absorb oxygen and ultimately give off 

 carbon dioxide and water. This respiration is unceasing and 

 is continued in all living members whether active or passive 

 until death ensues. If oxygen be entirely withheld, growth, 

 movement, irritability and activity in general ultimately 



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

 is wrong since all forms of respiration are essentially intra-molecular. 



