270 PHYSIOLOGY CHAP. 



(Gscheidlen). Langendorff (1885) first demonstrated that grey 

 matter also is alkaline to litmus intra vitam, and that the acid 

 reaction sets in after cutting off the blood -supply, and may 

 disappear again if the circulation is re-established promptly. The 

 observation that in the frog rise of temperature, strychnine 

 poisoning, or any cause that increases metabolism accelerates the 

 appearance of the acid reaction, led Langendorff to conclude that 

 the formation of acid is due to vital processes, the products of 

 which are eliminated under normal conditions by the blood stream. 



We owe our first detailed knowledge of the metabolic pro- 

 cesses that go on in the nerve-centres to the researches of Verworn 

 and his pupils (1900-3). The method used by Verworn in his 

 experiments on frogs consisted in replacing the blood circulation 

 by an artificial circulation of various fluids. This artificial 

 circulation, in the form either of a constant stream or of a 

 rhythmically intermittent current similar to that of the normal 

 circulation by means of a small pressure pump (Winterstein, 

 Baglioni), was introduced through a glass cannula, inserted in the 

 aorta, near the heart. After passing through the whole vascular 

 system the fluid left the body again at the cardiac orifices, which 

 were opened so as to allow the circulating fluid to escape through 

 them. Verworn used strychninised frogs for experiment because 

 their increased excitability made it possible to obtain a more exact 

 and easy demonstration of the changes in reflex activity caused by 

 the influence of various experimental factors. Briefly stated, his 

 results are as follows : 



If the blood of a strychninised frog is replaced by physiological 

 saline previously deprived of its oxygen by boiling, before the 

 circulation is started, the tetanic spasms that occur at every 

 contact gradually diminish and are separated from each other by 

 increasingly long pauses of inexcitability, till finally no reaction 

 can be aroused. On then circulating the oxygen-free saline there 

 is a slight initial recovery, which can only be explained by the 

 washing away of the toxic products of metabolism that have 

 accumulated. The recovery thus obtained is, however, incomplete 

 and of short duration. If, on the other hand, the salt solution is 

 replaced by well-oxygenated defibrinated blood, there is soon a 

 complete recovery shown by strong and protracted tetanic spasms. 

 What constituent of the blood is responsible for this complete 

 recovery of the normal excitability? Verworn found that the 

 recovery was practically the same when salt solution fully 

 saturated with oxygen was circulated instead of blood, while 

 blood serum deprived of oxygen was totally ineffective. This 

 shows that the restorative action was due not to organic nutritive 

 materials, but solely to the oxygen. 



On the strength of these results Verworn distinguishes two 

 fundamentally different factors in the paralysis of the centres, viz. 



