22 



BOYS AND GIRLS IN BIOLOGY. 



hot, and not to let it stand too near the fire. Take two 

 bottles and half fill them with sweetened water, or, what 

 is better, " Pasteur's fluid," 1 and sow just a drop or two 

 of yeast in each, heat them both till they boil, and as 

 they are cooling, cork them up with cotton, or " cotton- 

 wool," as the English say. Let them stand for a few 

 days, and there will be no signs of life in either, but if 

 you place just one of the torul^e into one of the bot- 



Fig. 16. 



Fig. 15. 



Bottle of Yeast corked up with Porous Jar containing Yeast, showing 

 Cotton. how the Fluids pass in and out, 



but the Cells do not. 



ties and cork it up again, the cell will begin to grow 

 and multiply, or ferment, till the bottle bursts. The 

 other bottle will remain perfectly quiet (Fig. 15) ; the 



Potassium phosphate 20 parts. 



Calcium phosphate 2 " 



Magnesium sulphate 2 " 



Ammonium tartrate 100 " 



Cane-sugar 1,500 " 



Water 8,376 " 



10,000 



