394 PHYSIOLOGY CHAP. 



that the oxidising processes acquire a greater degree of intensity, 

 and have been most studied. Active muscle breathes in excess of 

 resting muscle. Blood coming from the vein of a tetanised muscle 

 is dark in colour, and contains a minimal amount of oxyhaemo- 

 globin : while the blood which comes from a muscle that is resting, 

 or paralysed by section of its motor nerve, presents the normal 

 characters of venous blood, in which as we have seen the oxygen 

 content may exceed 15 vols. per cent of the blood. 



Again, when muscle is placed under conditions that prevent it 

 from absorbing oxygen, e.g. when it is brought into an atmosphere 

 of hydrogen or nitrogen, it continues to give off carbonic acid, and 

 for a certain time is capable of contracting (Hermann, see p. 68). 

 It would thus seem that muscle must be allowed the property of 

 taking up and storing oxygen in such a condition that it cannot 

 be removed by simple lowering of pressure. The oxygen required 

 for the formation of carbonic acid, given off by muscle in the 

 presence of nitrogen and hydrogen, is certainly derived from that 

 previously stored up and fixed in a compound similar to, but more 

 stable than, that into which it enters with haemoglobin, and which 

 has been wrongly termed intermolecular oxygen. 



According to recent work of Verworn, Baglioni, and H. 

 Winterstein (1900-1907), the tissue whose vitality is most strictly 

 associated with the action of free oxygen is the central nervous 

 system. Baglioni, e.g., found on isolating the frog's spinal cord 

 from the body after cutting out the circulation, and taking as the 

 index of its activity the reflex movements of a posterior limb, 

 connected with the cord by the sciatic nerve, that the reflex 

 activity of the cord is in strict ratio with the 9 tension of the 

 surrounding atmosphere. If placed in a moist chamber, through 

 which nitrogen is passed without a trace of oxygen, such a spinal 

 cord at a temperature of 15-20 C. ceases to exhibit reflexes after- 

 half to three-quarters of an hour. If it is then suddenly brought 

 back into the presence of oxygen, it recovers its vitality. On the 

 other hand, Baglioni succeeded in keeping alive the isolated spinal 

 cord of amphibia for a comparatively long period (forty-eight hours 

 and more) by placing it in a warm chamber through which pure 

 oxygen was circulated. This specifically high demand of the central 

 nervous system for oxygen explains the fact that in all cases of 

 asphyxia or lack of oxygen in the blood, the first tissue that feels 

 the toxic effects, and ceases its activities, is the central nervous 

 system (cerebral cortex, spinal cord ; see p. 70). We shall return 

 to this subject in Vol. III., in treating of the physiology of the 

 Qervous system. 



Moleschott enunciated the hypothesis that the oxygen passing 

 from the blood to the tissues is utilised in the constructive pro- 

 cesses, i.e. it enters into the most complex substances of the tissues, 

 which then, on splitting up, generate carbonic acid. Cl. Bernard 



