250 SECRETION. 



pressure of blood in the glands, though this undoubtedly 

 exerts an important influence. It is necessary that every 

 condition should be favorable to the act of secretion, for this 

 influence to be effective. Experiments have shown that 

 pain is capable of completely arresting the secretion of urine ; 

 operating undoubtedly through the nervous system. If, now, 

 the flow of urine be arrested by pain, an increase in the 

 pressure of blood in the part fails to influence the secretion. 

 To illustrate this fact more fully, Bernard divided the nerves 

 on one side, through which the reflex nervous action was 

 communicated to the kidney, leaving the other side intact. 

 He then found that increase in the arterial pressure, accom- 

 panied with pain, diminished the flow of urine on the sound 

 side, through which the nervous action could operate, and 

 increased it upon the other. 1 We have already alluded to 

 the experiments in which secretion was excited through the 

 nervous system, when the arterial pressure had been con- 

 siderably diminished. 



The influence of pressure of blood upon secretion may, 

 then, be summed up in a few words : There is always an in- 

 crease in the activity of secretion when the pressure of blood 

 in the glands is increased, and a diminution when the pres- 

 sure is reduced ; except when there is some modifying influ- 

 ence operating through the nervous system. 



Influence of the Nervous System on Secretion. The fact 

 that the secretions are generally intermittent in their flow, 

 being discharged in obedience to impressions which are made 

 only when there is a demand for the exercise of their func- 

 tions, would naturally lead to the supposition that they are 

 regulated, to a great extent, through the nervous system ; 

 particularly as it is now well established that the nerves are 

 capable of modifying and regulating local circulations. The 

 same facts apply, to a certain extent, to the excretions, which 



1 These experiments were detailed by Bernard in his lectures at the College 

 of France in the summer of 1861. 



