48 



the water supply, although we have never detected a case where the 

 parasitic species originated from this source. It is quite likely that 

 the infection comes more often through the nematode eggs contained 

 in the water and less often through the adult worm. The non para- 

 sitic nematodes are in general associated with all kinds of decay, and 

 all of our public water supplies which contain decomposing vegetation 

 furnish no doubt an environment for certain species of nematodes. 

 It is not improbable that the high temperatures recommended by 

 some for the control of nematodes were based upon experiments in 

 which care was not taken to prevent contamination, but it is more 

 likely that the large mass of soil employed was not heated evenly and 

 perhaps some portions fell below the requisite degree of temperature. 

 This is more likely to occur where defective methods of piping are 

 employed and also where the soil is piled up to a considerable depth, 

 in which case a thermometer thrust into the top layers of the soil 

 would not always indicate the temperature of some portions under- 

 neath. 



Methods of Sterilizing the Soil. 



Descriptions of methods of sterilizing the soil have not been very 

 numerous up to the present time. 



In 1892 Sturgis' recommended a method of heating soil for Aster 

 culture. In this case the plants were grown out of doors and the 

 roots became covered with galls probably through the introduction 

 of unfrozen soil or manure which was infested with the worm. It 

 can easily be seen that there are many difficulties in heating soil out 

 of doors to kill nematodes and when attempted on a large scale it 

 would not be practicable nor in this climate necessary, providing 

 proper precautions are taken . Should such a measure become 

 necessary, however, the method advocated by Dr. Sturgis might 

 be employed on a small scale. He recommends the application 

 of a device commonly used for drying earth in the prepara- 

 tion of asphalt pavements. It consists of a large piece of sheet 

 iron 6 or 8 feet square, raised from the ground. A wood fire is built 

 under this and the earth is thrown on and allowed to heat for 10 or 

 15 minutes. When this is completed the earth is removed and 

 another supply is placed upon it and heated for the same length of 

 time. A considerable quantity of earth can be heated in this way in 



I. Conn. Agr. Expt. Station Report, 1892, p. 48. 



