272 PHYSIOLOGY CHAP. 



Further advance in the general physiology of the nerve- 

 centres was made by Baglioni (1904) with his method of isolating 

 the spinal cord. This method is much simpler than that of 

 artificial circulation, and avoids the lesions caused by protracted 

 artificial circulation, which readily induce oedema and lower the 

 vitality of the nerve - centres. Baglioni's method consists in 

 dissecting out the spinal cord by removing the dorsal halves of 

 the vertebrae, and separating it from the rest of the body, so that 

 it is only attached by the sciatic nerve and plexus to the leg, 

 which can be stimulated and used as the index of excitability 

 on one or both sides. On applying mechanical or electrical 

 stimuli to the skin, reflex movements are produced in the leg, 

 since the spinal centres have not been injured by the operation. 

 Baglioni finds that on placing this preparation in an atmosphere 

 of pure oxygen, or in physiological saline saturated with oxygen, 

 it survives and preserves perfect reflex activity for twenty-four 

 to forty-eight hours. The oxygen tension of atmospheric air is 

 not enough to maintain its vitality for more than two hours at a 

 temperature of 18-20 C., as the oxygen can only be absorbed 

 from the dorsal surface of the cord the ventral surface being 

 covered by the anterior half of the vertebrae. Reflex action 

 disappears in a much shorter time, in about three-quarters of an 

 hour, if nitrogen is substituted for oxygen, and more rapidly in 

 proportion as the temperature is higher. 



This experiment indicates even more plainly than the last the 

 great oxygen hunger of the nerve-centres and their capability of 

 surviving for a comparatively long time with their circulation cut 

 off and with no supply of organic nutrient materials. The need 

 of oxygen, which greatly exceeds that of the peripheral nerves, is, 

 according to other experiments of Baglioni, a characteristic property 

 of the central nervous system, not only in vertebrates, but in in- 

 vertebrates also. 



Winterstein, Baglioni, and Fienga subsequently found that it 

 was possible to isolate the frog's cord still more completely by 

 lifting it almost entirely out of the vertebral canal. Total 

 isolation of the cerebrospinal axis is thus possible in the toad 

 (Baglioni, 1908), owing to the great length of the cauda equina, 

 which allows of the necessary manipulation in freeing the cerebro- 

 spinal axis from its connections without serious injury. Fig. 166 

 gives the photograph of such a preparation from the toad. 



Winterstein (1906) carried out a series of quantitative 

 estimations of the gaseous metabolism of the frog's isolated spinal 

 cord by means of Thunberg's microspirometer, which, as shown on 

 p. 231, makes it possible to measure the carbonic acid given off' and 

 the oxygen absorbed, thus giving the respiratory quotient for small 

 organs and animals. He concludes that the asphyxial paralysis 

 of the centres is due, not to the consumption of the reserve 



