1813.] Chemical Properties of Animal Fluids. • 381 



adhering to them, but soon it begins to decompose, its colour 

 changes by the influence of the air from white to yellow or 

 greenish, the warmth and moisture of the mouth contribute to 

 complete the decomposition, and the same earthy phosphates 

 which arc produced by oxidation and combustion in open fire are 

 here formed and slowly deposited on the surface of the tooth by 

 a slower but a similar process. The tartar is, therefore, as it 

 were, the ash of mucus crystallized on the tooth, and this, as is 

 *vell known, will in I ■ gthof time form very large incrustations. 

 I have found it to consist of the following substances : — 



Earthy phosphates 7^*0 



Mucus not yet decomposed 12*5 



Peculiar salivary matter 1 "0 



Animal matter soluble in muriatic acid 7' 5 



100-0 



S. The Mucus of the mucous Membranes. 



I shall premise some remarks on the term mucus, as applied 

 to animal chemistry. It properly signifies the mucus of the 

 nostrils ; but many chemists have extended it to other substances 

 found in the animal fluids ; so that Jordan, Bostock, Haldat, and 

 others, reckon it among the constituents of these fluids. None 

 of these chemists has considered mucus, used as a general term, 

 as identical with the nasal mucus, or, if they have thought so, it 

 has been a very great error. I must now mention that there is 

 no such principle as the mucus of animal fluids, the substance 

 «o considered being in reality lactate of soda mixed with the 

 animal matter that always accompanies it : but if it did exist as 

 a separate principle, some other term should have been used, to 

 distinguish it from the mucus of the nostrils, which is very 

 different. 



The chemists who have the most attended to the analysis of 

 mucus have been Messrs. Bostock, Fourcroy, and Vauquelin j 

 but none has given a very satisfactory account of its properties. 

 The two latter chemists, who have published a long memoir on 

 animal mucus, have too much generalized the characters pecu- 

 liar to nasal mucus, in attempting to extend them to the mucus 

 of the intestines and gall bladder, for example, where they are 

 totally inapplicable. 



The mucus of mucous membranes is produced from the same 

 KCretory organ throughout the body, and possesses every where 

 the same external characters which constitute vnu/is.- but in 

 chemical properties the mucus of different organs varies consi- 

 derably, according to the required use in protecting these organs 

 from the contact of foreign substances. Thus the mucus of the 

 nostrils and trachea, which is intended to protect these mem- 



