422 ALBUMINOUS COMPOUNDS. 



called albuminoids of which connective and elastic tissue, carti- 

 lage, and epithelium are composed. 



After serving their purpose in the organism, they are ex- 

 creted, not, however, in the form of albumin, but in that of 

 urea. It is extremely improbable that the}' are converted di- 

 rectly into urea, but rather into leucine and tyrosine, uric acid, 

 kreatin and kreatinine, and other sut^tances^ from which urea 

 is produced by further decomposition. Lately, some have 

 seemed inclined to put forth the opinion that peptones, after 

 their absorption, instead of being raised again to the rank of 

 albuminous bodies, undergo still further decomposition, and 

 yield hydro-carbons, which serve as fuel to the body, and nitro- 

 genous substances, which are rapidly converted into urea and 

 led, while the waste of the tissues proper is supplied by 

 albumin absorbed as such from the alimentary canal (Pick). 



* * 2. Preparation of a Solution of Albumin to be 

 used in testing. Egg Albumin. In order to get a solu- 

 tion of albumin for examination, pour the whites of two or three 

 hen's eggs into a beaker, and cut them up with a pair of scis- 

 sors, so as to liberate the albumin from the network of fine mem- 

 branes in which it is inclosed ; stir the viscous fluid vigorously 

 with a glass rod, and then press it through a piece of linen. 

 Mix it with an equal quantity of water, allow it to stand at 

 rest for some time, and then filter it. It passes very slowly 

 through the filter and chokes it very quickly. Several small 

 filters should therefore be used in preference to one or two 

 large ones, and they should be changed as soon as they get 

 choked. The filtration should also be quickened by the use of 

 the air-pump (see Appendix, 211). 



This filtrate contains inorganic salts as well as albumin, but 

 it will serve perfectly well to show most of the properties of 

 albumin. For some purposes, however, serum albumin is to be 

 preferred (xcf 18). 



* 3. Preparation of Pure Albumin. If pure albumin 

 is wanted, it may be prepared by separating the inorganic salts 

 from it by dialysis, and this operation is also useful in showing 

 that albumin does not diffuse. 



Before subjecting the diluted and filtered albumin to dialysis, 

 it is advisable to concentrate it by evaporation at 40 C., so as 

 to quicken the diffusion of the salts. Then place the concen- 

 trated liquid in a dialyser (App. 212), and let it remain over 

 distilled water. Change the water every six hours, till the water 

 no longer gives a turbidity with silver nitrate. As sodium 

 chloride is the chief salt contained in the egg albumin its ab- 

 sence in the dilfusate may be regarded as a sign that the albu- 

 min is free from all salts which diffuse. The vessels used must 

 be perfectly clean, and the distilled water tested beforehand, as 

 this test is very delicate. The albumin still retains a certain 



