146 Chapter IX 



heat is due to the liberation of energy caused by the stimulation 

 of the secretory fibres ; the challenge has come to the dilatator fibres. 

 Are there really such things, or is the dilatation a " functional dila- 

 tation " ? This question must arise from general considerations and 

 from special considerations. Generally there is reason to believe that 

 a functional dilatation accompanies functional activity; particularly 

 the proven functional dilatation of the vessels when adrenalin is 

 injected raises the question whether the same explanation does not 

 fully account for the chorda dilatation. 



I say " fully " because I think it will scarcely be challenged that, 

 even if there were no vaso-dilatator fibres in the chorda tympani, 

 there would be some degree of dilatation of a functional nature when 

 it is stimulated. The question then really is this : Is the dilatation 

 due to stimulation of the chorda tympani the result of two mechanisms 

 or of one ? If the dilatator fibre in the chorda is put on its trial, can 

 it prove its title ? 



Were I to act as its counsel and attempt this proof I would be 

 well advised to seek for some instances of dilatation, produced by 

 chorda tympani stimulation, which do not appear to involve the 

 functional activity of the gland. Two such may be cited. 



(1) The most obvious case for consideration is that of the atropin- 

 ised gland. The experiment is one of the best attested in physiology, 

 namely, that if atropin is administered intravenously in certain doses 

 saliva will not flow on stimulation of the chorda tympani, but dilata- 

 tion takes place. With smaller doses of atropin saliva is obtained; 

 with larger ones dilatation is not evoked, but between these extremes 

 you may get the dilatation without the secretion. If the flow of 

 saliva is the true index of the functional activity of the gland, the 

 title is proved. But it is not a foregone conclusion that some sub- 

 liminal degree of functional activity may not take place unless it 

 finds its expression in a flow of saliva. Therefore it is necessary 

 to measure the metabolism of the gland. The results of numerous 

 experiments of this character are summed up in the table on p. 147. 

 In every case there is some degree of increased metabolism when 

 the chorda tympani is stimulated. Certain criticisms of the experi- 

 ments which we have quoted may rise in the mind of the reader. 

 The first is that on comparing atropinised with unatropinised glands 

 the increased metabolism elicited by the stimulation is considerably 

 less in the former than in the latter. That is true, but it is also true 

 that the dilatation is not maintained in the atropinised glands in the 



