Respiration, Aeration, and Fermentation 295 



Considerable diversity may be manifest as to the extent of 

 this respiration, and in the case of germinating seeds, the 

 nature of reserve foods is an important factor in this 

 regard. In certain tissues, anaerobic respiration takes 

 place to such an extent as to be very readily recognized 

 by the usual demonstration of CO 2 production. Never- 

 theless, while CO 2 is commonly an end product of this 

 type of respiration, alcohol, lactic acid, hydrogen, and 

 other products may be identified with it. Since no free 

 oxygen is required, decomposition resulting in CO 2 and 

 the other products mentioned are obviously by rearrange- 

 ment of the atomic groups in the organic molecules. 

 This type of respiration is therefore truly anaerobic, or 

 without aeration. The term ' intramolecular ' has also 

 been employed in this connection. 



Anaerobic respiration in the tissues of higher plants may 

 be experimentally studied by use of germinating seeds, 

 preferably starchy seeds, such as barley and buckwheat, 

 but slices of potato or other solid tissues of this nature are 

 also useful. The essential apparatus is the same as for 

 aerobic respiration, but in this case it is necessary either 

 to exhaust all air with a first-class air pump, or else to 

 replace air with some gas which is physiologically inert. 

 Hydrogen was formerly used as a gas of this nature, but 

 as there is a possibility that it may be so injurious as to 

 introduce error, nitrogen may be substituted therefor. 



Attention has been drawn already to the fact (section 

 87) that anaerobic respiration of roots is found to result 

 in the production of traces of some excrete organic acids, 

 whereas, in aerobic respiration, C0 2 alone is evolved. All 

 of the results point to the conclusion, therefore, that by- 



