TO PRACTICAL PHYSIOLOGY. [l. 



(/?.) Add excess 'of absolute alcohol = a precipitate of peptone, 

 but not in a coagulated form. 



(i.) It is not precipitated by saturation with sodic chloride or 

 magnesic sulphate, nor by boiling with sodic sulphate and acetic 

 acid. 



(./.) Pure peptone is not precipitated by saturation with neutral 

 sulphate of ammonia. N.B. The other proteids are. Hence this 

 salt is a good reagent for separating other proteids, and thus leaving 

 the peptones in solution. 



(k.) It also gives Millon's test. 



(L) Diffusibility of Peptones. Place a solution of peptones in 

 a dialyser covered with an animal membrane, as directed in Lesson 

 I. i (D.) (ra.), and test the diffusate after some time for peptones. 

 Peptones do not diffuse through a parchment tube. 



(m.) Saturate the solution of commercial peptones with (NH 4 ) 2 

 S0 4 = a precipitate of albumoses or proteoses. Filter. The nitrate 

 contains the pare peptone. 



11. VII. Coagulated Proteids are insoluble in water, weak 

 acids, and alkalies, and are dissolved when digested at 35 to 40 C. 

 in gastric juice (acid medium), or pancreatic juice (alkaline 

 medium), forming first proteoses and finally peptones. They give 

 Millon's reaction. 



There are two subdivisions : 



(A.) Proteids coagulated by Heat. 



Preparation. Boil white of egg hard, and chop up the white. 



(a.) Test its insolubility in water, weak acids, and alkalies. 



(b.) It is partially soluble in acids and alkalies, when boiled for 

 some time. 



(c.) Bruise some of the solid boiled white of egg, diffuse it in 

 water, and test it with Millon's reagent. 



('/.) For the effect of the digestive juices see "Digestion." 



(B.) Proteids coagulated by Ferment Action. 



(i.) Fibr'n is insoluble in water and in weak solutions of 

 common salt. When prepared from blood, and washed, it is a 

 white, fibrous, soft, and very elastic substance, which exhibits 

 fibrillation under a high magnifying power (see " Blood "). 



(a.) Place well-washed fibrin in a test-tube, add o.i per cent, 

 hydrochloric acid. The fibrin swells up and becomes clear in the 

 cold, but does not dissolve. 



(ft.) Kepeat (a.), but keep on a water-bath at 60 C. for several 

 hours ; filter, and test the nitrate for acid-albumin by neutralisation 

 with very dilute potash. 



(c.) To a very dilute solution of copper sulphate in a test-tube, 

 add fibrin. The latter becomes greenish, while the fluid is 

 decolourised. Add caustic soda, the flake becomes violet. 



