5 o 4 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 he 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 Pfliiger, Arch./, d. ges. Physiol., Bonn, 1868, Bd. i. S. 6S6. 
- Gamgee, ''Physiological Chemistry," vol. ii.. from whom much of this paragraph 
is taken. 
: "Lecons de physiol. experimentale," 1856, Bd. ii. 
4 On injecting a large quantity of dextrose into the blood, I have found sugar in the 
saliva, and in quantity which is, 1 think, much too large to be accounted for by diffusion. 
5 Langlev and Fletcher, Phil. Tram.', London, 18S9, vol. clxxx. p. 149. 
,; Eckhard, Beitr. :. Physiol. C. Ludwiy, z. s. 70, Gcburtst., Leipzig, 1887, S. 13. 
