76 ELECTRO-PHYSIOLOGY CHAP. 



affected by the narcotic. Consciousness, conscious sensation, and 

 voluntary movement in short, all psychical activities in the 

 narrower sense are extinguished, while reflexes still continue. 

 Reflex function is next abolished, nerve, muscle, glands, etc., 

 remaining still unaltered. This explains why the vital functions 

 survive, and why at its early stages narcosis is not directly 

 dangerous to common vitality. The anaesthesia of the surgeon is 

 really incomplete ; it affects only the most susceptible elements 

 of the central nervous system, while the other excitable parts 

 (muscle, nerve, glands, etc.), although equally accessible to 

 narcosis, are attacked later, long after the functions of the nervous 

 centres have been abolished. Under all circumstances, however, 

 excitability and conductivity are indubitably functions of the proto- 

 plasm of the axis-cylinder in nerve-fibres also, a conclusion that 

 is significant in regard to certain theories to be discussed below. 



III. INFLUENCE OF VARIOUS CONDITIONS UPON EXCITABILITY 



OF NERVE 



If the effect of certain poisons thus leaves no doubt that the 

 central and conducting parts (cells and fibres) of the nervous 

 system differ essentially in their physiological properties, the same 

 conclusion is no less obvious from the consideration of many other 

 circumstances which influence the excitability and conductivity of 

 the nervous centres. Temperature is of the first importance ; its 

 marked action on the functions of all living matter is well 

 known. The fact that frogs exhibit differences of reflex excitability 

 at different temperatures, preserving it generally longer at low 

 temperature than at high, has long been familiar, but accurate 

 observations on the point are wanting, which is the more to be 

 regretted since the existing data are very contradictory. On the one 

 hand, it is affirmed that warming of the spinal cord to 24-27 C. 

 increases reflex excitability the more transiently in propor- 

 tion as the temperature is higher ; on the other hand, Tarchanow 

 and Freusberg find that when the trunk is packed with ice, the 

 reflexes discharged from the hind limbs are considerably augmented 

 a fact which, if true, recalls the effect of cooling on striated 

 muscle (supra}, as discovered by Gad and Heymans. The point, 

 in any case, requires further investigation. In the ganglion-cells, 



