ANIMAL OXIDATIONS. 459 



motion and excitability when in hydrogen, but became active when placed 

 in oxygen again. 1 Max Verworn 2 confirmed these observations on Rhizo- 

 poda of the Red Sea. It is difficult to perform such experiments upon 

 the cells of more highly organized forms, because they contain combined 

 oxygen, which enables the muscles, for example, to work for some time 

 with production of carbon dioxide in an atmosphere devoid of oxygen. 3 

 If, however, a muscle is allowed to act until exhausted, it is found that it 

 becomes active again, only when provided with a new supply of oxygen. 

 Such relations have been established for the muscles of the heart. Finally, 

 as is well known, E. Pfluger 4 has shown that frogs which were kept at low 

 temperatures in pure nitrogen gradually lost their excitability, but regained 

 it again, even after remaining twenty-four hours in this atmosphere, on 

 being placed in the air once more. We have to thank Max Verworn 5 for 

 a very interesting experiment in this direction. He replaced all the blood 

 in a frog with a physiological salt solution, containing . 6 to . 8 per cent. 

 The salt solution was free from oxygen. If now by injection of strychnine 

 the ganglion cells of the spinal medulla were excited, as much as possible, 

 then the neurons worked (under the constant streaming of salt solution) 

 until finally all the oxygen stores had been exhausted. In less than an 

 hour the reflex excitability is lost. After this the strongest irritation 

 produces no reflex action. If now a salt solution containing dissolved 

 oxygen is caused to circulate through the blood-vessels, the frog revives 

 within a few minutes, and again shows the increased excitability caused by 

 the strychnine. Every time the circulation of the salt solution containing 

 the dissolved oxygen is stopped, the ganglion cells at once become unex- 

 citable. The experiment may be repeated over and over again, with the 

 same frog. Since in this experiment the ganglion cells are not provided 

 with fresh nutriment, it is not possible to explain the action of oxygen by 

 the simple assumption that its absence prevents the complete combustion 

 of the decomposition products, while at the moment oxygen enters the 

 energy becomes available to the cells. To be sure, we are quite ignorant 

 concerning the work of the ganglion cells. We do not know what their 

 expenditure of energy is. It may be very small. If we remember that 

 the oxygen of itself is not able to attack the decomposition products from 

 the food, but requires assistance on the part of the cell before the oxygen 

 can find a point of attack, then it is not perfectly clear why the oxygen 



1 Untersuchungen iiber das Protoplasma imd die Kontraktilitat, Leipsic, 1864. Z. 

 Biol: 36, 425 (1898). 



J Die Bewegung derlebendenSubstanz. Jena, 1892. Cf. also Die Biogenhypo these. 

 Jena, 1903. 



3 Kronecker: Ueber die Ermiidung und Erholung der quergestreiften Muskeln 

 (1871). Joteyko: La fatigue et la respiration e'le'mentaire du muscle. Paris, 1896. 



4 Pfliiger's Arch. 10, 251 (1875). 



5 Arch. Anat. Physiol. 1900, Suppl. 152. 



