PHYSIOLOGY 



219 



be quantitatively determined from the increase in the weight of the caustic potash 

 by which it has been absorbed, or from the amount of barium carbonate precipi- 

 tated by conducting the respired carbonic acid through baryta water (to which 

 some BaCl 2 has been added). In this last experiment it will of course be 

 necessary to free the air from all traces of carbonic acid before it is admitted to the 

 respiring plants. 



Intramolecular Respiration. — In the middle of the seventies 

 Pfluger made the surprising 

 discovery that, frogs are not 

 only able to live for some time 

 in an atmosphere devoid of 

 oxygen, but even continue to 

 exhale carbonic acid. From 

 similar investigations it was 

 found that plants also, when 

 deprived of oxygen, do not die 

 at once, but can prolong their 

 life for a time and evolve car- 

 bonic acid. Under these cir- 

 cumstances it is apparent that 

 both elements, the carbon as 

 well as the oxygen, must be 

 derived from the organic sub- 

 stance of the plants themselves : 

 the oxygen can only be ob- 

 tained through some unusual 

 process of decomposition carried 

 on within the plant. This form 

 of respiration has consequently 

 been described as intramole- 

 cular. 



The amount of carbonic 

 acid produced in a given time 

 by intramolecular respiration is 

 usually less than that given off Fig. 191 

 in the same time during normal 

 respiration. There are plants, 

 however (for instance, Vicia 

 Faba), whose seedlings, in an 

 atmosphere of pure hydrogen, 

 will exhale for hours as much carbonic acid as in the ordinary air. 

 During intramolecular respiration all growth ceases and abnormal 

 processes of decomposition take place, whereby alcohol and other 

 products are formed. 



It had formerly been believed that the inciting cause of respiration was the 

 oxidising activity of the oxygen, which was thought to act upon the living 



Experiment in respiration. The inverted 

 flask (B) is partially filled with flowers, which 

 are held in place by the plug of cotton (W). 

 Through the absorption of the carbonic acid ex- 

 haled in respiration, by the solution of caustic 

 potash (K), the mercury (Q) rises in the neck of 

 the flask. 



