304 GENERAL PHYSIOLOGY 



the universe without beginning is life, and that, after the bodies 

 now termed inorganic had been separated out upon the cooling 

 surface of the incandescent planet by its intense vital activity, and 

 were not able to return again into the hot liquids which gradually 

 decreased in quantity because of the progressive decrease in 

 temperature of the earth's crust — we maintain that, after this 

 had occurred, protoplasm must necessarily have remained over. 

 The heavy metals, once organic elements, no longer melted, 

 and did not return into the circulation from which they had 

 .been cast out. They are the signs of the rigor mortis of the 

 'gigantic, cooling, primaeval organisms, whose breath perchance was 

 luminous iron-vapour, whose blood was liquid metal, and whose 

 food was meteorites." 



4. Pfliiger's Idea 



In one of the most suggestive works in physiological literature 

 Pflliger ('75,1) has discussed very fully the question of the origin 

 of life upon the earth, and has defended the idea of spontaneous 

 generation, that living substance originated upon the earth itself 

 out of lifeless substances. Pfliiger's ideas are especially valuable 

 in that in a strictly scientific manner he discusses the problem in 

 intimate connection with the facts of physiological chemistry, and 

 follows it out far into detail. 



The essential point of Pfliiger's investigation is constituted by 

 the chemical characteristics of proteid as that substance with 

 which life in its essentials is inseparably united. There exists a 

 fundamental difference between dead proteid, as it occurs, e.g., in 

 egg-albumin, and living proteid, as it constitutes living substance ; 

 this difference is the self-decomposition of the latter. All living sub- 

 stance is continually being decomposed, in some degree spontane- 

 ously and more through outside influences, while dead proteid under 

 favourable conditions remains intact for an unlimited time. The 

 chief condition of this decomposition is intramolecular oxygen, 

 i.e., the oxygen that occurs in the living proteid molecule, and 

 is continually being received by it from the outside through 

 respiration. That this oxygen is the essential condition follows 

 from the facts that during the decomposition carbonic acid is con- 

 tinually being formed, and that carbonic acid does not arise from 

 living proteid by direct oxidation of the carbon and a simple 

 splitting-off of the carbonic acid molecule, but by dissociation, i.e., 

 by an internal rearrangement of the atoms and the separation of 

 new atomic groups from one another. Living substance must 

 contain oxygen already in combination in the living molecule, 

 and in the decomnosition a rearrangement must take place, other- 

 wise it cannot be conceived how, as Pfliiger has shown upon frogs, 

 animals can exist longer than a day without free oxygen in an 



