CHEESE 371 



a razor, and press the smooth surface gently down on a clean 

 cover-slip, so as to leave an impression of the cheese upon it. 



Pass the slip through the flame and dip it in ether for two 

 minutes and then in absolute alcohol for one minute to remove 

 the fat. Stain for ten minutes with Nicolle's carbol-thionin 

 solution (saturated solution of thionin in 90 per cent, alcohol, 

 5 c.c. ; i per cent, solution of carbolic acid, 50 c.c.). Examine 

 with low and high powers. 



Note the forms of the bacteria present. Are they cocci or 

 rods? 



Are the organisms arranged in heaps or colonies, or distributed 

 singly ? 



Ex. 161. Try the above experiment with cheeses of different 

 ages. Make observations on the form and arrangement of the 

 bacteria in fresh, half-ripe, and fully ripe cheeses. 



(iv) Ripening of Soft Cheeses. The chief differences 

 between the hard and soft varieties of cheese have been 

 incidentally mentioned earlier in the chapter. To the 

 soft kinds no artificial pressure is applied, the whey in 

 the curd being merely allowed to drain away by gravita- 

 tion. Such cheeses, of which Camembert may be taken 

 as one of the best known examples, frequently contains 

 from 45 to 50 per cent, of water. On account of this 

 high moisture content, bacteria grow in them very 

 rapidly, and moulds soon cover their external surfaces. 



The chemical changes go on quickly, progressing from 

 the outside inwards, a partially ripened specimen show- 

 ing a firm core of .acid curd, around which is a layer 

 of buttery, semi-liquid or digested casein of variable 

 thickness. 



The casein is broken down into proteoses, peptones, 

 and amino-acids : the decompositions are similar in kind 

 to those found in the ripening of hard cheeses, but they 



