6 THE SECRETIONS: 



essential oils, but more sparingly soluble in water. It alone 

 possesses the characteristic odour of saliva ; it is unaffected by 

 galvanism and by most of the reagents which coagulate albumen. 

 It is abundantly precipitated by sub-acetate of lead and nitrate 

 of silver ; feebly so by acetate and nitrate of lead, and tincture 

 of galls; uninfluenced by bichloride of mercury and strong 

 acids ; the latter considerably heighten its proper odour and 

 impair its solubility, whilst alkalies render it more soluble, and 

 give it the smell of mucus. Moderate heat and oxygen gas 

 also increase its odour, but a more intense heat or cold dimi- 

 nishes or entirely destroys it. At a suitable temperature, 

 ptyalin may be preserved for any length of time without risk 

 of decomposition. The salivary fluid from which ptyalin has 

 been removed, possesses a sickly mucous smell, decomposes 

 much sooner than ordinary saliva, and, in the process of decay, 

 invariably evolves ammonia. If the fluid be heated, the mucous 

 smell will be increased until the evaporation shall have been 

 continued nearly to dryness, when a slight salivary odour may 

 be recognized, due to a portion of ptyalin being liberated from 

 the mucus with which it was previously in combination." 



Dr. Wright says that sulphocyanogen is an invariable consti- 

 tuent of healthy human saliva. He advises that it be sought 

 for in the alcoholic extract of the residue left by the careful 

 evaporation of the fluid, as the mucus, unless removed, offers 

 considerable impediment to the action of reagents. The sulpho- 

 cyanogen occurs in combination with potassium, the salt consti- 

 tuting generally from -051 to -098 of the secretion. "The 

 proportion," he says, " is temporarily augmented by local sti- 

 mulation of the salivary glands, as by smoking, chewing siala- 

 gogues, &c. It is also increased by the internal use of prussic 

 acid and salts of cyanogen, and remarkably so by the use of 

 sulphur." 



Pure saliva absorbs a variable quantity of oxygen. Dr. 

 Wright says, " I have known the quantity absorbed to exceed 

 2i times the bulk of the saliva ; but I once met with an instance 

 in which the healthy secretion did not absorb more than half 

 its volume of oxygen. The difference is generally dependent 

 upon the carbonic acid gas naturally contained in the saliva, 

 the proportion of which gas to the secretion varies from one 

 eighth to one twelfth in volume, though, in some particular 



