94 



PRACTICAL PHYSIOLOGY, 



[XIII. 



(r.) Test with iodine after neutralisation with sodic carbonate 

 and filtration = no glycogen. 



(d.) Test for grape-sugar = much sugar. 



After death the glycogen is transformed into grape-sugar unless 

 precautions be taken to prevent this transformation (p. 91). 



LESSON XIII. 

 MILK, FLOUR, AND BREAD. 



1. Milk. Use fresh cow's milk. 

 (a.) Examine the " naked-eye " characters of milk. 

 (#.) Examine a drop of milk microscopically, noting numerous 

 small, highly-refractive oil-globules floating in a fluid (fig. 48). 



(i.) Add dilute caustic soda. The globules run into groups, 

 (ii.) To a fresh drop add osmic acid. The globules first become brown and 

 then black. 



(iii.) If a drop of colostrum is obtainable, observe the "colostrum cor- 

 puscles " (fig. 48, 0). 



(c.) Test its reaction with 

 litmus paper. It is usually 

 neutral or slightly alkaline. 



(d.) Take the specific gra- 

 M vity of perfectly fresh un- 

 skimmed milk with the 

 lactometer. It is usually be- 

 tween 1028-1034. Take the 

 specific gravity next day after 

 the cream has risen to the 

 surface, or after the cream 

 is removed. The specific 



c 



gravity is increased (1033-37) 

 by the removal of the lightest 

 constituent the cream. 



(e.) Dilute milk with ten 

 The times its volume of water, 

 carefully neutralise it with 

 dilute acetic acid, and observe 

 that at first there is no precipitate, as the caseinogen is prevented 

 from being precipitated by the presence of alkaline phosphates 

 (Lesson I.). Cautiously add acetic acid until there is a copious 



sr-a 



FIG. 48. 



48. Microscopic Appearance of Milk, 

 upper half, M , is milk ; the lower half, colos- 

 trum, C. 



