15 



We do not mean to assert that tliese formulae represent the 

 actual constitution of the respective tissues^ but only that they 

 give the proportion of elements actually present, and show how 

 they might give rise to those tissues. Some of these tissues con- 

 tain protein, or at least yield it by the action of potash, whilst 

 others, as for instance the gelatinous tissues, although doubtless 

 derived from protein compounds, do not contain it, and conse- 

 quently cannot yield it. 



Diagnosis of protein. Its insolubility in water, alcohol, and 

 ether, and its precipitation fi'om an acid solution by the ferro- 

 cyanide and ferridcyanide of potassium are sufl&cient. 



2. Albumen. 



This important modification of protein forms the white of 

 eggs, and occurs in large quantity in all the animal fluids that 

 contribute to the nutrition of the organism. It is also found in 

 most of the animal solids, and in nearly all morbid products. 

 We have abeady adverted to its existence in the vegetable 

 kingdom. 



Albumen is naturally soluble in water, and it is found dis- 

 solved in the serum of the blood, in vegetable juices, &c. But 

 when it has once been submitted to a certain degree of tem- 

 perature, or to the action of various chemical reagents, it assumes 

 the coagulated state, and becomes insoluble in water. 



Soluble albumen. Soluble albumen may be obtained in a 

 solid form by evaporating to dryness, at a temperature not ex- 

 ceeding 120°, the serum of the blood, or white of egg. The dry 

 mass is yellow, partially transparent, hard, and tough ; it must 



