fatigue due to the accumulation of the toxic products of meta- 

 bolism, and exhaustion due to consumption of the supply of 

 oxygen. The former can be eliminated by mechanical washing, 

 the latter, on the contrary, only by a fresh supply of oxygen to the 

 centres. The paralysis caused by these two factors together 

 produces what Verworn terms work-paralysis. 



Verworn attributes fatigue to the production and accumulation 

 of carbonic acid, more particularly on the strength of Winterstein's 

 experiments. This author found that C0 2 at a high concentration 

 is able to exert a markedly paralysing action on the centres, and 

 inhibits the appearance of the strychnine spasms. 



By the method of artificial circulation Winterstein endeavoured 

 to decide whether this narcosis, since it is capable of suspending 

 excitatory processes, is able to check the restorative action of oxygen 

 also. He experimented as follows : 



A strychninised frog, asphyxiated by the circulation of oxygen- 

 free salt solution, was anaesthetised by the circulation of salt 

 solution containing a narcotic (chloroform, ether, alcohol, carbonic 

 acid). Oxygenated blood mixed with the same narcotic was then 

 circulated. Under these conditions there was of course no 

 recovery of the centres, on account of the narcosis. But on 

 circulating normal saline to remove the drug there was still no 

 recovery of central excitability, because the asphyxiated nerve- 

 centres, which had been deprived of oxygen, were unable, owing 

 to the action of the narcotic, to utilise it when offered them. 

 Narcosis thus suspends not only the katabolic but also the anabolic 

 processes. Fr. W. Frohlich observed an analogous effect on peri- 

 pheral nerve (supra, p. 231). This important fact is explained 

 by the latest work of Winterstein (1905) as a direct arrest of 

 the oxidation processes by narcotics, represented in the lower 

 organisms by an extraordinary fall in the consumption of oxygen 

 during narcosis. 



In another series of researches Winterstein studied the special 

 state of the nerve-centres known as heat paralysis. When a frog 

 is warmed in a thermostat, all reactions disappear after a period 

 of general excitation, owing to a paralysis of the nerve-centres 

 which passes off if the animal be cooled again in time. Winterstein 

 found this heat paralysis to be closely related to the oxygen 

 supply of the centres. If a frog which is in a condition of heat 

 paralysis be cooled in an atmosphere free of oxygen, or if its 

 blood be replaced by cold physiological saline containing no 

 oxygen, the animal is unable to recover from the paralysis. 

 Recovery, on the contrary, takes place when there is sufficient 

 oxygen. It follows that heat paralysis must be a form of asphyxia, 

 due, according to Winterstein, to the fact that either the store of 

 oxygen in the centres or their oxidative processes are insufficient 

 for the excessive demand produced by the heat. 



