338 PROTEIN-COMPOUNDS. 



fluids, as for instance urine, not unfrequently deposit, on heating, 

 a dense, amorphous precipitate, showing no trace of albumen, and 

 consisting only of phosphates. This is often the case when the 

 urine is very slightly acid, but the precipitate may be distinguished 

 from coagulated albumen by the addition of a mineral acid, which 

 readily dissolves the earths, or by acidulating the urine, before 

 boiling, with a little acetic acid, when no precipitate will any 

 longer be obtained by boiling, if its presence were dependent 

 on the earthy salts of the urine. 



In testing animal fluids, and especially those of a pathological 

 nature, we must particularly observe the form in which the 

 albumen coagulates, for on this, as has already been observed, 

 numerous other relations depend ; thus, a flocculent coagulum that 

 admitted readily of being collected on the filter, would show that 

 the albumen is not combined with an alkali, and that the latter 

 must have been extracted from it by an acid, since, in the normal 

 state all the albuminous fluids of the body contain albumen in 

 combination with an alkali, and coagulate like milk, or in a white, 

 opaque jelly. Again, if, on evaporation, an animal fluid from 

 which the albumen has previously been removed by boiling, become 

 covered with a thin, colourless membrane, we have no right to 

 conclude, as is so frequently assumed, that casein is present, but 

 simply that the fluid still contains sufficient alkali to prevent 

 the ordinary coagulation of the albumen, and, in short, that 

 although a portion of the alfiumen may have been removed by 

 boiling, the fluid yet contains the so-called albuminate of soda or 

 potash. 



Morbid blood and exudations frequently contain pure albumen 

 that has been dissolved merely by salts ; from these fluids the 

 greatest part of the albumen may be precipitated by dilution with 

 large quantities of distilled water, first as a milky turbidity, and 

 finally in flakes, as was first shown by Scherer. 



In the determination of albumen it must always be recollected that 

 we are unable to distinguish it from the similar protein-compounds 

 with that scientific accuracy with which we are able to recognise 

 most other organic substances. We may, indeed, indicate the 

 differences presented by the individual reactions in similar sub- 

 stances; but albumen unfortunately occurs in several modifications, 

 sometimes resembling one and sometimes another protein-compound, 

 while neither the determination of the saturating capacity nor the 

 elementary analyses of these bodies present any marked differences. 

 Our determination of the albumen in an animal fluid must there- 



