78 THE SECRETIONS : 



an acid : the latter has, however, lost the characteristic vis- 

 cidity of mucus. If the acid be removed by means of an alkaline 

 carbonate, the mass does not become viscid; if, however, in- 

 stead of a carbonate, a caustic alkali is employed, the viscidity 

 is restored. If the mucus of the gall-bladder is precipitated 

 by alcohol, the viscidity disappears, it is restored, however, by 

 being washed in water. When dried, it becomes transparent 

 and yellow ; on the addition of water it swells, and is rendered 

 opaque but not viscid. 



5. Mucus from the urinary bladder. 



Vesical mucus is always present in the urine, but only in 

 very small quantity in the normal secretion. In recently dis- 

 charged urine it cannot be detected with the naked eye, but 

 after the fluid has stood for some time, there are formed light, 

 often hardly perceptible nebulae of sinking mucus, in which the 

 microscope reveals mucus-corpuscles and epithelium-cells. On 

 nitration the mucus remains on the paper in the form of co- 

 lourless flocculi ; it contracts and ultimately forms a glistening 

 varnish-like coating, which does not resume its former appear- 

 ance on being moistened with water. 



According to Berzelius it is insoluble in sulphuric acid, but 

 the greater part of it dissolves in acetic and hydrochloric acids : 

 ferrocyanide of potassium throws down a precipitate from these 

 solutions. 1 



Morbid Mucus. 



It is well known that any irritation will increase the secretion 

 of mucus in an extraordinary degree ; this is seen in the 

 secretion of the mucous membrane of the nostrils and lungs 

 during a common cold or catarrh. The mucus is then mate- 

 rially changed ; at the commencement of the attack it is gene- 



1 [We have at present analyses of only three varieties of mucus, viz. the mucus of 

 the oviduct of frogs, the mucus of the oesophagus of the peculiar species of swallows 

 which build edible nests, and the mucus of the gall-bladder. The results differ so 

 much that either animal mucus is a variable mixture of heterogeneous substances, or 

 that different substances at present bear the name of mucus in common. The ana- 

 lyses are quoted in Mulder's Chemistry of Vegetable and Animal Physiology, p. 240, 

 English translation.] 



