Septembee 16, 1910] 



SCIENCE 



369' 



into combination. On the uumanured plot 

 the crop is so largely removed that the 

 little root and stubble remaining does not 

 provide material for much fixation. 



Though numerous attempts have been 

 made to correlate the fertility of the soil 

 with the numbers of this or that bacterium 

 existing therein, no general success has 

 been attained, because probably we meas- 

 ure a factor which is only on occasion the 

 determining factor in the production of 

 the crop. Meantime our sense of the com- 

 plexity of the actions going on in the soil 

 has been sharpened by the discovery of 

 another factor, affecting in the first place 

 the bacterial flora in the soil and, as a con- 

 sequence, its fertility. Ever since the ex- 

 istence of bacteria has been recognized 

 attempts have been made to obtain soils in 

 a sterile condition, and observations have 

 been from time to time recorded to the ef- 

 fect that soil which has been heated to the 

 temperature of boiling water, in order to 

 destroy any bacteria it may contain, had 

 thereby gained greatly in fertility, as 

 though some large addition of fertilizer 

 had been made to it. Though these obser- 

 vations have been repeated in various 

 times and places they were generally ig- 

 nored, because of the difficulty of forming 

 any explanation: a fact is not a fact until 

 it fits into a theory. Not only is steriliza- 

 tion by heating thus effective, but other 

 antiseptics, like chloroform and carbon 

 bisulphide vapor, give rise to a similar re- 

 sult. For example, you will remember 

 how the vineyards of Europe were de- 

 vasted some thirty years ago by the attacks 

 of phylloxera, and though in a general 

 way the disease has been conquered bj' the 

 introduction of a hardy American vine 

 stock which resists the attack of the insect, 

 in many of the finest vineyards the owners 

 have feared to ri.sk any possible change in 

 the quality of the grape through the intro- 



duction of the new stock, and have re- 

 sorted instead to a system of killing the 

 parasite by injecting carbon bi-sulphidc 

 into the soil. An Alsatian vine-grower 

 who had treated his vineyards by this 

 method observed that an increase of crop 

 followed the treatment even in cases where 

 no attack of phylloxera was in question. 

 Other observations of a similar character- 

 were also reported, and within the last five 

 years the subject has received some con- 

 siderable attention until the facts became- 

 established beyond question. Approxi- 

 mately the crop becomes doubled if the soil 

 has been first heated to a temperature of 

 70° to 100° for two hours, while treatment 

 for forty-eight hours with the vapor of 

 toluene, chloroform, etc., followed by a 

 complete volatilization of the antiseptic, 

 brings about an increase of 30 per cent, or 

 so. Moreover, when the material so grown 

 is analyzed, the plants are found to have- 

 taken very much larger quantities of nitro- 

 gen and other plant foods from the treated 

 soil; hence the increase of growth must be 

 due to larger nutriment and not to mere 

 stimulus. The explanation, however, re- 

 mained in doubt until it has been recently 

 cleared up by Drs. Russell and Hutchin- 

 son, working in the Rothamsted laboratory. 

 In the first place, they found that the soil 

 which had been put through the treatment 

 was chemically characterized by an ex- 

 ceptional accumulation of ammonia, to an 

 extent that would accoimt for the increased 

 fertility. At the same time it was found 

 that the treatment did not effect complete 

 sterilization of the soil, though it caused at 

 the outset a great reduction in the numbers 

 of bacteria present. This reduction was 

 only temporarj', for as soon as the soil was 

 watered and left to itself the bacteria in- 

 creased to a degree that is never attained 

 under normal conditions. For example, 

 one of the Rothamsted soils employed con- 



