94 PROXIMATE ANALYSIS OF 



In tliis case heat will develop a pellicle on the surfacCj and 

 acetic acid will throw down a precipitate, which is soluble 

 in an excess of the test : the acid must therefore be added 

 with caution. 



It must not however be forgotten that if much albuminate 

 of soda, and at the same time no free albumen be present in 

 the fluid, no coagulation will occur on the application of heat, 

 but a pellicle will be formed on the surface. This is however 

 a case of very rare occurrence, and the difficulty may be 

 readily solved by the addition of acetic acid which will precipi- 

 tate casein but not albumen. If a fluid which contains 

 casein presents a whitish turbid appearance (as for instance, 

 milk, the milky fluid which is found in the breasts during the 

 later stages of pregnane}^, the urine in certain pathological 

 states, &c.) the presence of butter, and in most instances, of 

 sugar, may be inferred. 



If the ferrocyanide of potassium does not produce any tur- 

 bidity in the fluid which has been previously acidulated with 

 dilute hydrochloric acid, no protein-compound is present. 



2. If the addition of acetic acid to the fluid renders it 

 turbid, or throAvs down a precipitate, which does not redissolve 

 in an excess of the test, then ppn or mucini is present. In 

 this case, a copious precipitate, insoluble in an excess of the 

 test, is thrown down by alum. In order to show that the 

 precipitate contains no casein, we may dissolve it in dilute 

 hydrochloric acid, and add ferrocyanide of potassium : no pre- 

 cipitate will be thrown down.2 



3. If allantoin, uric acid, or hippuric acid are suspected 

 to be present, a considerable quantity of the fluid must be 

 boiled in order to coagulate any albumen that may be present, 

 and must then be filtered and evaporated to one fourth of its 

 original volume. Fluids of this nature are generally of a 

 yellowish colour, may be either clear or turbid, and may or 

 may not contain albumen. 



In the examination of the allantoic fluid, crystals of allan- 

 toin are gradually formed, which, after being purified by 



' [Mucin is the peculiar animal matter of mucus ; a brief notion of its leading cha- 

 racters is given in the chapter on the " Secretions of Mucous Membranes."] 



'■^ As chondrin and glutin are not constituents of any of the animal fluids, we have 

 deemed it uniiecessarv to notice them in the text. 



