78 ELECTRO-PHYSIOLOGY CHAP. 



once abolish the functions of the central nervous system. The 

 entire blood-supply of a frog may even, as Cohnheim pointed out, 

 be replaced by physiological salt solution, and the normal functions 

 of the nerve-centres will none the less continue unchecked for 

 hours at a moderate temperature. If the experiment is inordi- 

 nately prolonged, the reflex functions are gradually extinguished. 

 But even when the aorta has been obstructed for hours, or after 

 prolonged exposure to a deoxygenated atmosphere, the frog will 

 recover completely. The functions of the great nerve-centres are 

 first attacked, and much later, the peripheral excitable parts (nerve 

 and muscle). The different elementary constituents tissue-ele- 

 ments again are variously sensitive to the cutting-off of the blood- 

 supply, and resulting changes in metabolism. Some die quickly, 

 as the gray matter of brain and cord ; others more slowly, as the 

 peripheral nerve-trunks and muscles. In warrn-blooded animals 

 the phenomena are essentially the same, but they occur much more 

 rapidly; here, too, the central system is first to die, and then the 

 peripheral nerves and muscles. This is true, both of anaemia, and 

 of the asphyxia due to poverty of oxygen in the blood. Stenson's 

 experiment is a good illustration of the first of these. If the 

 abdominal aorta is ligatured in a warm-blooded animal, paralysis 

 of the hind limbs occurs in a few minutes, although excitability 

 and conductivity of nerve-trunks and muscles remain perfectly 

 normal. 



The dependence of the central nerve-cells upon the blood is 

 indicated in the anatomical distribution of vessels within the 

 white and gray matter of the central organs, as well as by 

 the vascular poverty of the peripheral nerves. It is known, 

 moreover, that a protracted interruption of the blood -supply 

 induces more or less definite histological changes in the ganglion- 

 cells of the gray matter of the spinal cord in warm-blooded 

 animals : these may even disappear altogether (degenerate), while 

 the fibres of the white matter are still intact (36). 



The facts thus briefly summed up show that the organ of 

 reflexes, the automatic central structure of the brain and spinal 

 cord, differs in a marked degree (and that by a whole series of 

 characteristic peculiarities in excitability and conductivity), if not 

 fundamentally, from other excitable parts of the nervous system. 

 The central nerve-cells are peculiarly susceptible to certain poisons. 

 Strychnin specifically affects, the excitability of the ganglion-cells 



