COMPOSITION OF HUMAN SALIVA. 211 



line ; although, under certain abnormal conditions of the system, it has occasionally been 

 observed to be neutral, and sometimes, though rarely, acid. We have occasionally ob- 

 served a distinctly acid taste in the saliva after very severe, prolonged, and exhausting 

 muscular exertion. The saliva becomes slightly opalescent by boiling or on the addition 

 of the strong acids. The addition of absolute alcohol produces an abundant whitish, 

 flocculent precipitate. Almost invariably the mixed saliva presents a more or less intense 

 blood -red tint on the addition of a per-salt of iron, which is due to the presence of a 

 sulpho-cyanide either of potassium or sodium. 



A number of analyses of the human mixed saliva have been made by different chem- 

 ists, presenting, however, few differences, except in the relative proportions of water 

 and solid ingredients, which are probably quite variable. One of the most reliable of 

 these analyses is the following, by Bidder and Schmidt : 



Composition of Human Saliva. 



Water 995'16 



Epithelium 1'62 



Soluble organic matter 1-34 



Sulpho cyanide of potassium 0*06 



Phosphates of soda, lime, and magnesia 0*98 



Chloride of potassium ) 

 Chloride of sodium \ ' 



1,000-00 



The organic principle of the mixed saliva, called by Berzelius ptyaline, is not affected 

 by heat or the acids, but, on the addition of an excess of absolute alcohol, is coagulated 

 in the form of whitish flakes, which may be readily separated by filtration. This sub- 

 stance has been closely studied by Mialhe and is described by him under the name of 

 animal diastase. This author regards it as the active principle of the saliva. It is ob- 

 tained from the human saliva by the following simple process : 



The fluid from the mouth is first filtered, then treated with five or six times its weight 

 of absolute alcohol, by which a white or grayish-white precipitate is formed. This sub- 

 stance is collected on a filter and is dried in thin layers on a plate of glass in a current 

 of air at from 100 to 120 Fahr. It may then be preserved indefinitely in a well-stop- 

 pered bottle. The principle thus prepared may be dissolved in water, when it is insipid, 

 neutral, and becomes readily decomposed, giving rise to a substance resembling butyric 

 acid. It has no influence upon the nitrogenized alimentary principles, but, when brought 

 in contact with raw or hydrated starch, readily transforms it, first into dextrine, and 

 afterward into glucose. According to Mialhe, the energy of this action is such that one 

 part is sufficient to effect the transformation of more than two thousand parts of starch. 



The presence of a certain quantity of sulpho-cyanide of potassium in the mixed saliva 

 can be demonstrated by the addition of a per-salt, especially the perchloride of iron. 

 That this is a constant and normal ingredient of the human saliva cannot be doubted. 

 We have frequently had occasion to apply this test to the saliva of different persons, and 

 the results have been invariably the same. 



It has been a question whether the red color produced by the perchloride of iron be 

 really due to the presence of a sulpho-cyanide in the saliva ; or, if it exist at all, whether 

 this salt be a normal constituent or be developed accidentally as a pathological condi- 

 tion, or produced, as has been suggested, by the action of reagents. The elaborate in- 

 vestigations of Longet seem to have settled these questions conclusively. He obtained 

 nearly three quarts of human saliva, which he collected in half an hour from forty sol- 

 diers, fasting, who, after having rinsed and cleaned the mouth, excited the secretion by 

 chewing pieces of India-rubber. The fluid was then concentrated so that all the sulpho- 

 cyanide was brought into a few drops, which showed, in an intense degree, the peculiar 



