NERVOUS CONTROL OF SECRETINC! GLANDS. 47 



now in a position to pick out, with clearness and precision, the funda- 

 mental truths of the earlier researches, to grasp the cause of their 

 want of success, and from their historical teaching to draw precepts for 

 the performance of an ideal experiment which shall definitely answer 

 our question. 



We have three commonly employed methods by means of which the 

 existence of nervous control over any organ may be determined. First, 

 we can cut through, or in other way paralyse, certain nerves which 

 are in anatomical connection with the part in question, and then submit 

 the organ to accurate observation in order to determine whether its 

 activity has been suspended or increased, or in any other way made 

 to deviate from the normal, either quantitatively or qualitatively. 

 Naturally our conclusions regarding the relations between the nerve 

 and the organ will be all the more accurate, and come nearer the truth, 

 the more completely and perfectly we compare the two conditions. A 

 second and striking proof of the existence of a nei-vous influence over 

 an organ is afforded by the results of excitation of its associated nerve. 

 When the stimulation calls forth each time the same alterations of 

 function, and when these at once disappear on cessation of the stimulus, 

 we may rightly and justly look upon this nerve as governing the 

 organ. Even here, however, one must not disregard the possibility 

 of two contingencies. It may occur that the function of the organ 

 suffers no alteration because the nerve or the organ is placed under 

 abnormal conditions, and in view of the defects which still, unfortu- 

 nately, cling to many of our physiological methods, this is very possible. 

 For this reason, experiments with a negative result enjoy only a very 

 qualified reputation, and by many authors are never published. On the 

 other hand, the alterations of function which appear in an organ on 

 stimulation of this or that nerve may have been brought about in- 

 directly through the intervention of one, or several other organs. Only 

 a careful and complete physiological (and where necessary anatomical) 

 isolation of the organ can guard us from this source of error. 



There is still a third mode of proof which, perhaps, should have 

 been more correctly given in the first instance. It furnishes evidence 

 of a nervous influence even where the first direct method remains 

 fruitless. This consists in the most general evidence of relationship 

 between the organ in question and the nervous system. It is nothing 

 more special than making accurate observations in the clinique and 

 in everyday life. The well-known fact of salivation at the sight of 

 appetising food has in this way always been accepted as a sound proof 

 of nervous influence over the salivary glands. 



Into this path research also wandered when the innervation of 

 the gastric glands was brought under investigation. 



