THE VITAL PHENOMENA OF BACTERIA. 115 



thod, others to the other. In the decomposition 

 of dead organic substance, a process which in 

 the form of putrefaction and decay is an inter- 

 mediate link in the cycle of animal and plant 

 life, certain species are better fitted to break 

 down the complex compounds present at the 

 start while others, work up the end products. 

 According to the discoveries of Heraeus, 

 Hueppe and Winogradsky the nitrifying bac- 

 teria are best fitted for the last part of the 

 process ; and the iron and sulphur bacteria 

 stand next above in the series. 



Through the beautiful investigations of Hell- 

 riegel and Wilfarth we know that in the root 

 tubercles of the Leguminosa and some other 

 plants, bacteria are found which have entered 

 into an intimate union or symbiosis with these 

 plants. By their aid the plants are able, 

 even when growing upon poor soil, to avail 

 themselves of atmospheric nitrogen for the 

 synthesis of proteids, while their chlorophyl 

 enable them to use synthetically the carbon 

 dioxide of the atmosphere. This discovery 

 has been turned to good account and marks 

 one of the notable advances in agriculture. 

 By inoculation of the soil with material con- 

 taining the bacteria of the root tubercles, and 

 likewise by cultivation of the useful plants upon 

 which these microbes are symbiotic, the yield 



