Chap - viii Respiration 42 , 



was held to combine directly with carbon to produce this 

 exhaled compound. The idea was not a strange one, as 

 the only facts observed up to that time were the entry of 

 oxygen and the exhalation of the carbon dioxide. At fust, 

 indeed, the formation of water was not known, only the 

 gaseous interchange involving oxygen and carbon dioxide 

 having been considered. The time was marked by a vast 

 amount of ill-directed research which was devoted to estab- 

 lishing a ratio between the exhaled carbon dioxide and 

 the absorbed oxygen, and to inquiries into the way this 

 ratio, the so-called respiratory quotient, is influenced by 

 various external conditions, and how it varies in different 

 organs at the different stages of their growth. With such 

 a hypothesis underlying the inquiry, there is little cause 

 for wonder that very contradictory results were reached, 

 and that little accurate knowledge of the respiratory process 

 was obtained. 



The identity of respiration with a combustion of some 

 kind was supported by suggestions as to what particular 

 constituents of the food were concerned. Sachs held that 

 it was carried on, at any rate in germinating seeds, ex- 

 clusively at the expense of the non-nitrogenous reserve 

 materials, a view which was very prevalent among the 

 animal physiologists of the time, and which led them to 

 classify foodstuffs as flesh-forming and heat-giving or 

 respiratory respectively. This view was opposed by some 

 observers, particularly Borodin, who, in 1878, suggested 

 that the nitrogenous substances constituting the proto- 

 plasm become oxidized, and to this oxidation is due the 

 appearance of asparagin in the plant, while the non- 

 nitrogenous materials are used up in supplying plastic 

 material to the protoplasm. 



Borodin's views were in a sense a reflection of the hypo- 

 thesis of Pfliiger, which had been stated a few years before 

 and which will be discussed a little later. The idea oi 



