2 PRACTICAL PHYSIOLOGY. [l. 



1. Preparation of a Solution of Egg- Albumin Soluble in 

 Water. Place the unboiled white of an egg in a porcelain capsule 

 (taking care that none of the yolk escapes), and cut it freely many 

 times with scissors to disintegrate the membranes, and thus liberate 

 the albumin. Add twenty volumes of distilled water, shake the 

 mixture vigorously in a flask until it froths freely. Cork the flask 

 and invert it, mouth downwards, over a porcelain capsule ; the 

 froth and debris float to the surface, and, after a time, if the 

 cork be gently withdrawn to allow the fluid to escape, a slightly 

 opalescent fluid is obtained. The opalescence is due to the pre- 

 cipitation of a small quantity of globulins. If the fluid be too 

 opalescent, strain through flannel or several folds of muslin. Such 

 a solution filters slowly, so that it is better to employ several small 

 filters if a clearer solution be required. If the fluid be alkaline, 

 neutralise it with 2 per cent, acetic acid. Egg-white contains about 

 11-12 per cent, of egg-albumin, together with small quantities of 

 globulins, grape-sugar, and mineral matter. 



General Reactions. (A.) Colour Reactions. 



(a.) Xanthoproteic Reaction. Add strong nitric acid = a 

 white precipitate, which on being boiled turns yellow. After cool- 

 ing add ammonia = the yellow colour or precipitate becomes orange. 



(b.) Millon's Test = a whitish precipitate which becomes brick- 

 red on boiling. A red colour of the fluid is obtained if only a 

 trace of proteid be present. 



Preparation of Millon's Reagent. Dissolve mercury in its own weight of 

 strong nitric acid, specific gravity 1.4, and to the solution thus obtained add 

 two volumes of water. Allow it to stand, and afterwards decant the clear 

 fluid ; or take one part of mercury, add two parts nitric acid, specific gravity 

 1.4 in the cold, and heat over a water-bath till complete solution occurs. 

 Dilute with two volumes of water, and decant the clear fluid after twelve 

 hours. 



(c.) Piotrowski's Reaction. Add excess of strong solution of 

 caustic soda (or potash), and then a drop or two of very dilute solu- 

 tion of cupric sulphate (1 per cent.) = a violet colour. The reaction 

 occurs more quickly if heat is applied, and the colour deepens. 



The peptones and albumoses give a rose-pink colour, instead of a 

 violet, if only a trace of copper sulphate is used. 



(B.) Precipitation. Peptones and albumoses are exceptions in 

 many cases. 



(d.) The solution is precipitated by (i.) lead acetate; (ii.) mer- 

 curic chloride; (iii.) picric acid; (iv.) strong acids, e.r/., nitric; (v.) 

 tannin ; (vi.) alcohol. 



(e.) Make a portion strongly acid with acetic acid, and add 

 potassic ferrocyanide = a white precipitate. 



(/.) Saturate it with ammonium sulphate by adding crystals of 



