iv GENERAL PHYSIOLOGY OF NERVOUS SYSTEM 267 



If the block is kept up for longer, no functional recovery takes 

 place. 



These facts, showing that the individual ganglion cells present 

 different resistances to anaemia, are confirmed by Landergren's 

 work on the phenomena of acute asphyxia. As shown in Fig. 165, 

 four stages can be distinguished in acute asphyxia. In the first 

 stage there is a brief rise of activity in the vasornotor bulbar 

 centre. When the activity of this centre ceases the excitation 

 of the vagal cardiac centre reaches its maximum. The course of 



I. II. III. IV. 



Period of general Period of suspended Period of exagger- Final period (pre- 

 excitation. respiration. ated respiration. mortal). 



FIG. 165. Diagram of vital resistance of some nerve-centres to asphyxia. (Landergren.) The 

 continuous curved line indicates the functional excitation and subsequent paralysis of the 

 bulbar vasomotor centre ; the dotted line, the functional state of the centre for the cardiac 

 vagus ; the broken line, the state of activity of the respiratory centre ; the dotted and broken 

 line (with which the life of the animal expires) indicates the functional state of the spinal 

 and vasomotor centres. 



the excitation of the respiratory centre was not, owing to a long 

 pause in respiration, completely represented, but it appears to 

 coincide approximately with that of the bulbar cardiac centre. 

 The last to be thrown into excitation are the spinal vasomotor 

 centres, the activity of which continues even when the function of 

 the other centres is abolished. 



That the metabolism of the nerve-cell is highly active in com- 

 parison with the very low metabolism of the nerve-fibre, appears 

 not only indirectly from the fact that the nucleated portion of the 

 cell is the trophic centre of the entire neurone, as we saw in 

 discussing Wallerian degeneration (see pp. 233 et seq.\ but also 

 and -more directly from the observation of Marinesco, that under 

 certain normal or morbid conditions of the ganglion cells there is 



