FUNCTIONS OF THE NERVE CELL 573 



Stenson's experiment of clamping the abdominal aorta teaches us also that 

 the nerve cells in the spinal cord very soon suffer from the lack of blood. 

 The posterior extremities become paralyzed soon after the aorta is closed off, 

 not because of the absence of blood in those parts but because of its absence 

 from the spinal cord. 



Fredericq has investigated these phenomena more closely and has reached 

 the following conclusions for the dog: Some fifteen to twenty seconds after the 

 clamp is applied a temporary excitation of the motor cells begins, but within 

 thirty to forty seconds the motor paralysis is complete. Up to this time the 

 sensibility of the posterior parts is entirely unaffected; but after one and one- 



Final All 



Gaspings Respirations 



Stopped 



FIG. 257. The relative resistance of several nerve centers in asphyxiation, schema, after Lander- 



gren. , the vasomotor center in the medulla; , the cardiac inhibitory center; 



_ ? the respiratory center; , the vasomotor center in the spinal cord. 



half minutes a hypersesthesia sets in, followed by anaesthesia, which is complete 

 at the end of three minutes. If now the clamp is removed, sensibility returns in 

 five to ten minutes, but motility somewhat later. By continuing the occlusion 

 long enough the paralysis and ansesthesia become permanent. 



From these facts we reach the very important conclusion that different 

 nerve cells have very different powers of resistance to anemia. 



Other observations go to show that the endurance of different nerve cells 

 under acute asphyxiation is very different. The schema in Fig. 257 repre- 

 sents, according to Landergren, the relative excitability and resistance through- 

 out the different phases of asphyxia of the following centers : the bulbar vaso- 

 motor center, the cardiac-inhibitory center, the respiratory center, and the 

 spinal vasomotor center (cf. page 238). The bulbar vasomotor is first ex- 

 cited and has the least resistance. When the activity of this center begins 

 to decline the cardio-inhibitory center has reached the height of its irrita- 

 bility. The course which is run by the irritability of the respiratory center 

 cannot be represented fully, owing to the respiratory pause which comes in, 

 but it seems to agree in the main with that of the vagus center. The spinal 



