ii EXTERNAL DIGESTIVE SECRETIONS 75 



paralytic secretion always makes its appearance. It can also 

 be provoked by the injection of small doses of curare into the 

 glandular arteries. It ceases in apnoea, and increases in dyspnoea. 

 After heinisection of the cord, paralytic secretion appears in the 

 gland of the opposite side also (Heidenhain). The interpretation of 

 these facts is very doubtful. Langley believes that the excit- 

 ability of the central end of the chorda increases after section, so 

 that it reflexly influences the secretion of both glands. 



(i~) A series of striking experimental data prove that the 

 salivary secretion excited by the activity of the nerve depends 

 essentially upon altered metabolism of the secretory cells, and 

 not on alteration of the blood-supply to the gland. Secretory 

 activity excited from the nerve persists for a certain time after 

 all the blood-vessels to the gland have been occluded, and even 

 after decapitation of the animal (Ludwig, Czermak, Giannuzzi). 

 On the other hand, when a mercury manometer is introduced into 

 the excretory duct of the submaxillary gland, and the chorda 

 tympani excited, secretion continues, even when the pressure in 

 the excretory ducts of the gland rises to a height considerably in 

 excess of that in the carotid artery. The pressure in Wharton's 

 duct may rise to 200 mm. Hg, while that of the carotids is not 

 above 122 mm. Hg. This shows that the stream from blood- 

 vessels to lymphatics, and from these to the glandular spaces, is 

 not merely independent of the pressure, but actually occurs 

 against the laws of filtration (Ludwig). 



(&) We have already seen that the injection of even small 

 doses of atropine and daturine suffices to abolish the secretory 

 activity of the chorda tympani (Keuchel). But if the state of the 

 glandular blood-vessels is watched during stimulation of the nerve, 

 it is found that their active dilatation is in no way hindered by 

 atropinisation (Heidenhain). We must therefore assume that the 

 chorda contains secretory fibres as distinct from the vaso-dilators. 

 Atropine paralyses the former and leaves the latter unaffected. 



(I) When a substance that paralyses the activity of the 

 secretory cells, e.g. a dilute solution of hydrochloric acid, or of 

 sodium carbonate, is injected into Wharton's duct, and the chorda 

 tympani subjected to prolonged stimulation, all secretion is 

 arrested and there is marked oedema of the gland from congestion 

 of lymph (Giannuzzi). This shows that the dilatation of the 

 arteries is capable of promoting the filtration of the lymph, but 

 not its penetration into the gland spaces. 



(m) Unilateral excision of the chorda tympani in puppies has 

 as a remote effect a marked diminution in weight of the corre- 

 sponding submaxillary, which may amount to 50 per cent. There 

 is at the same time a reduction in the volume of the mucous cells 

 and the serous cells, which form the crescents or demilunes of 

 Giannuzzi (G. Bufalini). 



