468 NATURE STUDY AND LIFE 



Small as bacteria are, they possess powers of growth 

 and multiplication not paralleled by any other living forms. 

 It is estimated that if all the oceans were nutrient broth, 

 with an average depth of one mile, the progeny of one 

 microbe might fill them full in less than five days. 



By precise methods it is possible to rear as pure a cul- 

 ture of a desired kind of bacteria as of any garden plant. 

 While we shall not be able to do this, we may make a num- 

 ber of instructive observations if we are on the alert and 

 know what to look for. The phosphorescence of decay- 

 ing wood, fish, or meat is due to bacteria of decom- 

 position. The red color, known in superstitious times as 

 the '* bleeding Host," that sometimes overspreads bread 

 and other foods, is caused by other harmless bacteria. 



It will be difficult or impossible, without expensive 

 microscopes, to distinguish bacteria from yeasts and 

 moulds. Still, a few simple experiments may be tried. 

 We may use our vials again, — this time filled with hay 

 infusion 1 or with a dilute, perfectly clear broth. We may 

 sterilize, as before described, by boiling on two succes- 

 sive days, and then sow a minute quantity of dust from 

 the schoolroom or the street, keeping other vials stop- 

 pered with cotton for comparison. The vials in which 

 dust is sown will soon grow turbid, a scum will form on 

 top, and an offensive odor of decomposition will probably 

 make it necessary to wash the vials out before the experi- 

 ment has continued too long. A boiled potato cut in two 



1 Hay infusion is made by soaking a handful of hay in a quart of warm 

 water for an hour and filtering. Bread water, potato water, or meat juice 

 diluted — any clear solution containing a little organic matter — will serve 

 the purpose. 



