43 CURBENT FOECE CHAP. IV. §. rH. 



the blood, as already advanced in the previous 

 Sections with respect to the other secretions ? 



The amount of deviation of the needle being 

 small, may be referred to the same causes as were 

 observed to exist with regard to the acid secretions 

 and fluids in the stomach. The secretion, urine, 

 being acid, counter currents arise and are produced 

 by the reaction of the acid of the urine upon 

 the fluids and substances with which it comes 

 into contact. In judging, therefore, of the effects 

 upon the needle, we must take into consideration 

 the acting points in the circuit; there may be at 

 least three acting points in a circuit, viz. at the 

 point of secretion, and at each of the electrodes. If 

 the direction of the current consequent upon secretion 

 coincide with those that occur at the electrodes, then 

 an increased effect upon the needle is necessarily 

 produced ; but if these currents tend to go in oppo- 

 site directions, then the result upon the needle will 

 be merely the differential effect. Hence we should 

 be led to very erroneous conclusions, judging merely 

 from the effect upon the needle, either as to the 

 force of the current, or its origin. 



Sufficient evidence has been obtained to warrant 

 the following deduction, viz. that when the electrodes 

 of a galvanometer are brought into contact, one with the 

 urinary secretion and the other with the venous blood 

 from the same part, an effect upon the needle occurs 

 indicating the blood and the urine to be in opposite 

 electric states. 



