CELL-CONTENTS AND CELL-WALLS. 4l 



(s) Dry the clotted albumin of a hard-boiled egg, mix it with 

 about twice as much powdered soda-lime, and add a little water to 

 form a paste of the mixture. Roll this paste between the fingers 

 into small pellets, and place these in a dry warmed tube of hard 

 glass. Heat over a Bunsen, and into the mouth of the tube place 

 first (A) a moist red litmus paper, then (B) a lead acetate paper. 

 The escaping vapours turn A blue and B black ; the former change 

 is due to ammonia (which can also be smelt), the latter to the for- 

 mation of lead sulphide proving the presence of nitrogen and of 

 sulphur in the albumin. 



(t) Put a bit of hard-boiled egg on a needle, and hold in a Bunsen 

 flame ; it becomes charred, showing that carbon is present. 



42. Froteoses and Peptones. These derivatives of 

 proteins ( 40) are formed in nature by the action of pro- 

 teolytic enzymes (pepsin, trypsin) on the primary proteins. 

 It is doubtful whether they occur as reserve food in resting 

 seeds, but they appear when germination begins. 



The proteoses (soluble in water, not coagulated on boil- 

 ing, but precipitated by acids) are intermediate digestion 

 products between primary proteins and the peptones 

 (soluble in water and neither coagulated by boiling nor 

 precipitated by acids). The peptones are readily soluble 

 in water, and are not precipitated by acids, alkalis, neutral 

 salts, and many of the other reagents that precipitate the 

 primary proteins. The proteoses are less diffusible than 

 the peptones ; some proteoses are not readily soluble in 

 water, and they are distinguished from peptones by being 

 precipitated when their solutions are saturated with ammo- 

 nium sulphate. Proteoses yield precipitates with many of 

 the reagents that precipitate other proteins ; the precipitates 

 they give with nitric acid, and with potassium ferrocyanide 

 in presence of acetic acid, disappear on warming and 

 reappear on cooling. 



43. Experiments with Commercial Peptone. Get some 

 Witte Peptone, which in reality contains more proteose than true 

 peptone. Dissolve in warm water, and make the following tests for 

 proteose and for peptone, after dividing the solution into portions 

 in test-tubes. 



(1) Heat the solution and acidify it with dilute acetic acid no 

 coagulation. (2) Saturate with ammonium sulphate a white pre- 

 cipitate, which partly disappears on heating and reappears on 



