504 THE SALIVAR Y GLANDS. 



sodium carbonate ; calcium carbonate and calcium phosphate are kept 

 in solution by the excess of carbonic acid, and precipitated as the gas 

 escapes. 



Saliva yields to a vacuum about twenty vols. per cent, of carbonic 

 acid, and small quantities of oxygen and nitrogen ; 1 the carbonic acid, 

 however, is all or nearly all combined with sodium carbonate to form 

 sodium bicarbonate. 



In the saliva of man, potassium sulphocyanate is normally present. 2 



The alkalinity of saliva depends upon the presence of sodium 

 carbonate. In man and in the dog the percentage of this salt varies 

 from 0*08 to 019 per cent. 



In disease, 2 traces of other substances have been found in the saliva 

 of man, for example, urea and leucine. In diabetes, lactic acid has been 

 found in the saliva; the presence of sugar has been denied by most 

 observers, but affirmed by some. In jaundice, saliva does not usually 

 contain either bile acids or bile pigments, but in some instances traces 

 are said to occur. In cases of poisoning with salts of mercury, lead, and 

 some other metals, small quantities of the salts may be present in 

 saliva ; it is stated, however, that the salts of arsenic are not secreted by 

 the salivary glands. 



An investigation into the character of the substances which can and 

 which cannot be secreted by the salivary glands, would undoubtedly 

 lead to interesting and valuable information. It is possible that, with 

 bodies not acted on chemically, the size of the molecule is the determin- 

 ing factor. A beginning of such inquiry, though not from this point of 

 view, was made by Bernard. 3 He experimented on the secretion from 

 the submaxillary and parotid glands of the dog, and on the parotid 

 glands of the horse. He found that potassium iodide was very readily 

 secreted, whilst neither sugar, 4 ferrocyanide of potassium, nor lactate of 

 iron was secreted by the salivary glands, though they were all secreted 

 by the kidney. Iodide of iron, on the other hand, passed into the saliva. 



When lithium citrate is injected into the blood, the spectrum of 

 lithium can be detected in the first drops of saliva secreted. 5 And 

 methylene-blue also passes into the saliva, but it does not appear to do 

 so constantly. Sulphindigotate of soda, which is so readily secreted by 

 the liver and kidney, is not secreted by the salivary glands; 6 after 

 injecting large amounts into the blood, a small quantity may be found 

 in the saliva, but there is no reason to believe that this is due to any 

 cause other than diffusion. 



EFFECTS OF THE CRANIAL AND SYMPATHETIC NERVES ON THE 

 BLOOD FLOW. 



The fundamental fact that the cranial nerve contains vaso-dilator 

 fibres and the sympathetic vaso-constrictor fibres, has been already 

 mentioned. If any salivary gland be exposed, it will be seen to flush on 



1 Pflttger, Arch.f. d. gcs. Physiol., Bonn, 1868, Bd. i. S. 686. 



2 Gamgee, "Physiological Chemistry," vol. ii.. from whom much of this paragraph 

 is taken. 



;; " Lefons de physiol. expe'rimentale," 1856, Bd. ii. 



4 On injecting a large quantity of dextrose into the blood, I have found sugar in the 

 saliva, and in qiiantity which is, 1 think, much too large to be accounted for by diffusion. 



5 Langley and Fletcher, Phil. Trans.', London, 1889, vol. clxxx. p. 149. 



6 Eckhard, Beitr. z. Physiol. C. Ludwiy, z. s. 70, Geburtst., Leipzig, 1887, S. 13. 



