134 Blood Flow and Secretion 



so far produced sufficient to disprove, beyond doubt, the existence 

 of special vasodilator fibres in the chorda contributing to the vaso- 

 dilatation, as assumed by Hilton and Lewis? The validity of the 

 conclusions drawn from the botulinum toxin experiments depends 

 on the specificity of this agent in paralysing cholinergic fibres. 

 Further, the delayed vasodilatation after arterial occlusion indi- 

 cates that a stable vasodilator agent appears when the gland cells 

 are excited by chorda stimulation or injected acetylcholine; but 

 they do not exclude the possibility that in addition injected acetyl- 

 choline, or acetylcholine released from dilator endings in such a 

 way as not to be antagonized by atropine, has a vasodilator action 

 of its own even if via kallikrein. There are some observations 

 which suggest that the blood vessels of the submaxillary gland 

 do have a supply of parasympathetic fibres. Histological investiga- 

 tions show that after degeneration of the sympathetic fibres there 

 are still nerve fibres left in relation to the vessels of the submaxil- 

 lary gland of the rat (Glimstedt and Hillarp, 1942) and of the cat, 

 dog and monkey (Kuntz and Richins, 1946). The words of Bar- 

 croft in his monograph The respiratory function of the blood (1914) 

 may still be applicable to the problem: "The answer then to the 

 question, 'Is it possible to demonstrate that the vaso-dilatation 

 which follows upon stimulation of the chorda tympani involves a 

 definite neuro-muscular vaso-dilator mechanism?' is 'It is not pos- 

 sible on the evidence at hand either to prove or disprove it'. The 

 functional dilatation involved may be held to account for all known 

 cases of dilatation in the submaxillary, but it is not proved to do 

 so. — It is not impossible that under normal circumstances dilata- 

 tion may be instituted by dilator fibres and maintained by meta- 

 bolic products." 



The latest contribution to the discussion comes from Terroux, 

 Sekelj and Burgen (1959). They estimated simultaneously the rate 

 of secretion, of blood flow and of oxygen consumption in submaxil- 

 lary glands of dogs. The effects of varying the frequency of stimu- 

 lation of the chorda and of atropinization were studied. During 

 secretory activity there was an approximately linear relationship 

 between the rate of saliva flow and the extra oxygen consumption, 

 but a poor correlation between oxygen consumption and blood 

 flow. Atropine depressed both the rate of saliva flow and the extra 

 oxygen consumption associated with it, in doses which had no effect 

 on the vasodilator response ; compared with the response to iden- 



