46 THE STORY OF THE BACTERIA. 



only by a night, is to melt a bit of the ice, mix 

 it with our culture gelatin, and in a day or two 

 we shall have a whole garden of growing 

 plants, which we can study at our leisure. 



Among the most curious things which the 

 bacteriologist has to exhibit in his bacterial 

 conservatory is the color-forming species. It 

 is only when they are growing in masses, of 

 course, that enough color is formed to be visi- 

 ble ; but then one may see in the little slimy 

 masses which cover the surface of the food or 

 culture media in the tubes, every color of the 

 rainbow and many variations in hue. Some- 

 times not only is the bacterial mass itself 

 brilliantly colored, but some of the chemical 

 substances which they form as they grow 

 permeate the gelatin and give it a beautiful 

 fluorescence, green or red. 



The writer was not long ago standing be- 

 side a supper-table, whose sole floral decora- 

 tion was a bunch of large, exquisitely tinted 

 chrysanthemums, when a friend remarked upon 

 the patience and skill which had been required 

 to develop this magnificent flower by artificial 

 selection from its simple and homely ancestor, 



