1 64 SCIENCE PROGRESS 



Other proofs of the existence of intramolecular oxygen are 

 mostly of the type first brought forward by Engelmann in 1868. 

 Engelmann kept ciliated epithelial cells in an atmosphere of 

 hydrogen till all movement ceased, and then added sufficient 

 oxygen to start the movements again. On replacing this mixed 

 atmosphere with pure hydrogen, it was found that cessation of 

 ciliary movement ensued earlier than on the first occasion. The 

 longer the cells were kept in oxygen, however, the longer time 

 did the ciliary movements persist in the hydrogen, so it looked 

 as if the cells had been able to store up a supply of intra- 

 molecular oxygen on which they could gradually draw. Again, 

 Ohrwall found that if the flow of perfusion liquid through an 

 excised frog's heart (kept in a hydrogen atmosphere or in salt 

 solution) were stopped, the heart ceased beating in one to three 

 hours. If the perfusion were resumed, the heart speedily began 

 to beat again ; but if the perfusion were now stopped it ceased 

 beating in four to twenty-five minutes — i.e. in a very much 

 shorter time than previously. 



Experiments of a similar nature have been made by Bernard 

 upon fish, and by Frohlich and by Baglioni upon nerve ; but, as 

 Winterstein points out, none of these results afford convincing 

 proof of the existence of intramolecular oxygen. Winterstein, 

 indeed, denies the existence of this oxygen, and he supposes that 

 the loss of excitability produced by deprivation of oxygen is due 

 to the accumulation of toxic products of fatigue. In the presence 

 of free oxygen, these products are gradually oxidised and 

 rendered harmless, and so it follows that if the inexcitable 

 tissue be exposed to oxygen for only a short time, but small 

 amounts of the toxic products are oxidised, and so a second 

 deprivation of oxygen induces a much speedier loss of excita- 

 bility than the original deprivation did. This explanation might 

 be held to be negatived by an interesting experiment of Verworn's, 

 in which a frog was perfused with oxygen-free salt solution. 

 Strychnine was added to the saline so as to heighten the excita- 

 bility of the cord, and for some minutes each stimulation of the 

 skin resulted in a succession of brief reflex muscular contrac- 

 tions. If during this initial period the flow of oxygenless saline 

 were stopped, the cord speedily lost its reflex excitability ; but if 

 the flow were resumed again, it was found that the excitability 

 might return for a short time. It then disappeared perma- 

 nently so long as the flow of oxygenless saline was continued, 



