1 64 CHE MIS TR V FOR A GRIC UL TURAL STUDENTS 



Procure some fresh blood. Notice that after a very few 

 minutes' exposure to the air the blood spontaneously coagu- 

 lates, a *' clot " containing the fibrm being formed, while the 

 " serum," containing blood albumin, separates. Enclose the 

 clot in a muslin bag tied over the nozzle of a water tap, and 

 allow water to run through, constantly kneading it with the 

 hand meanwhile until the red colouring substance is washed 

 away, and the fibrin is left white. 



Procure some raw meat. Note that the solid matter is 

 already insoluble and coagulated. Knead it in a muslin bag 

 under water until colourless myosin is obtained. 



The albuminoids are then all characterised by this property 

 of coagulation, but while fibrin and myosin spontaneously 

 coagulate, albumin only coagulates on heating or upon the 

 addition of acid, and casein, which does not coagulate on 

 heating, does so on the addition of either acid or rennet. 

 The albuminoids are further distinguished as a class by the 

 property of peptonisation, i.e. the conversion of the coagulated 

 albuminoids into soluble compounds termed peptones. This 

 chemical change may be brought about by dilute acids, but it is 

 most easily effected by certain soluble ferments acting in some 

 cases in acid, and in some cases in alkaline liquids. 



Cut a little of the white of a boiled egg into thin strips, and 

 mix with a solution of pepsin (a soluble ferment found in the 

 gastric juice of the stomachs of animals) in dilute hydrochloric 

 acid, and digest for a few hours at a temperature of 36° C. 

 (blood heat). Note that the albumin dissolves. Boil the liquid : 

 coagulation no longer occurs ; the albuminoid has been con- 

 verted into a soluble peptone. 



The solutions of albuminoids and peptones are further dis- 

 tinguished by their behaviour on diffusion. To illustrate liquid 

 diffusion or osmose, securely tie pieces of parchment paper over 

 the mouths of two thistle funnels. Run into the one funnel a 

 solution of magenta and into the other a solution of cochineal, 

 and then place the inverted funnels in beakers of distilled water. 



