110 THE DIGESTIVE FLUIDS. 



Qualitatively, as has just been stated, the normal mixed saliva is 

 of fairly constant composition. The quantitative variations which 

 may occur in health are seen from the following analyses of human 

 saliva, which are taken from Hammarsten : 



Frerichs. Berzelius. Ilaramerbacher. 



Water 994.1 992.9 994.2 



Solids 5.9 7.1 5.8 



Mucus and epithelium 2.13 1.3 2.2 



Soluble organic matter 1.42 3.8 1.4 



Inorganic salts 2.19 1.9 2.2 



Potassium sulphocyanide .... 0.10 . . 0.04 



An analysis of the inorganic' salts, moreover, calculated for 1000 

 parts by weight of mineral ash, gave the following results : 



Potassium 457.2 



Sodium 95.9 



Oxide of iron 50.11 



Oxide of magnesium 1.55 



Sulphuric acid (as SO 3 ) 63.8 



Phosphoric acid (as P 2 O 5 ) 188.48 



Chlorine 183.52 



The albumins proper of the saliva are said to be similar to those 

 of the blood-serum, but are present in only very small amount. 

 They may, in fact, be regarded as accidental constituents, as the 

 greater portion of the albumins which enter into the composition of 

 the glandular cells is no doubt transformed into the specific secretory 

 products of these glands, viz., into mucin and the amylolytic fer- 

 ment ptyalin. In the cells proper, however, these substances appar- 

 ently do not exist as such, but as mucinogen and ptyalingen, which 

 are later transformed into mucin and ptyalin, respectively. As a 

 matter of fact, it is possible to obtain the inactive ptyalinogen from 

 the solids of the horse, and to transform it artificially into the active 

 ferment. To this end, it is only necessary to collect the saliva from 

 the parotid gland of the horse under antiseptic precautions, and to 

 prevent the further access of micro-organisms. A secretion is thus 

 obtained which is perfectly inert when brought in contact with 

 starch solution, while a corresponding specimen that has been ex- 

 posed to the air at once begins to manifest the specific activity of 

 free ptyalin. Of the manner in which this transformation is effected 

 in the mouth, w r e are as yet ignorant, but it appears that the bacteria 

 which are here normally present are of importance. Similar results 

 are reached when the finely hashed glands are extracted with chloro- 

 form-water, until the active ferment can no longer be obtained in 

 this manner. On subsequent treatment witli a very dilute solution 

 of acetic acid other extracts can then be obtained, which are as active 

 as the first, thus showing that a substance must have been present 

 which could not be isolated with the chloroform-water, but which 

 can be transformed into ptyalin by means of acetic acid. 



Ptyalin. The ptyalin or salivary diastase, as it is also termed, is 

 an amylolytic ferment, and as such capable of causing the inversion of 



