96 Prof. W. Pfeffer. The Nature and 



Although such energetic physiological combustion involves a very 

 considerable production of heat, yet in consequence of the extensive 

 radiating surface, only a slight rise of temperature usually ensues. 

 The functional metabolism, in fact, as in poecilothermic organisms, 

 does not provide for the regulative maintenance of a definite body- 

 temperature. At the same time the plant is adapted to accom- 

 modate itself to temperatures, ranging for example, from 2 to 

 40 C., and to bear such oscillations of the body-temperature with- 

 out injury. Manifestly it is altogether expedient that, when the tem- 

 perature rises, tlie activity of growth and respiration should be simul- 

 taneously accelerated. On the other hand, the fact that when the 

 optimum temperature for growth has been exceeded, substances are 

 burnt up by respiration, in an ever increasing degree, while the pro- 

 cesses of growth, and movement are retarded or altogether stopped, 

 is a non-adaptive phenomenon, determined only by the absence of 

 any regulative check. 



As long as the external conditions remain constant, however, respi- 

 ration is always regulated by the plant, and is in general increased, 

 as the activity of the whole organism automatically rises. This 

 happens, for example, when a plant begins to grow again, after com- 

 pleting the winter's rest, or when a traumatic reaction is called 

 forth in consequence of injury. Thus, if we cut a potato in pieces, 

 the production of carbonic acid gradually increases nine- or ten-fold, 

 in the course of twenty-four hours, owing to the respiratory process, 

 and then gradually diminishes again as the traumatic reaction passes 

 off. Here the plant falls as it were into a state of fever, for simul- 

 taneously with respiration, the production of heat is very considerably 

 augmented. 



If we bear in mind that the essential office of functional metabo- 

 lism, consists in providing, by means of chemical transformations, 

 the necessary energy for vital action, we cannot be surprised that 

 this end is not always attained in the same way. Apart from the 

 fact that different carbon-compounds are consumed in respiration, and 

 that not only carbonic acid, but in certain plants oxalic acid, acetic 

 acid, citric acid, &c., arise as the final products of physiological 

 combustion, there exist even aerobic organisms in which kinetic 

 energy is no longer obtained by the oxidation of any carbon compounds 

 whatever. Among these are the nitrobacteria, some of which oxidise 

 ammonia to nitrous acid, while others oxidise nitrous to nitric acid ; 

 these remarkable organisms, with the help of the energy thus gained, 

 are at the same time capable of constructing their organic food 

 synthetically from carbonic acid. Again, in the respiratory process 

 of the sulphur-bacteria, the sulphuretted hydrogen undergoes com- 

 bustion, sulphur being first set free, and then oxidized to form sul- 

 phuric acid. Thus, in these organisms, sulphuric acid is secreted as 



