46 



to heat is not so great as the spores of bacteria and fungi. In the 

 case of nematodes we have not only to kill the adult worm which is 

 not remarkably protected against heat and desiccation, but also its 

 eggs which are able to offer considerable more resistance to the vari- 

 ovis elements, inasmuch as they are provided with a more protective 

 membrane. Nevertheless there is nothing about the structure of a 

 nematode egg which would render it so impervious to heat as some of 

 the smaller spores which every bacteriologist has to deal with in ster- 

 ilizing his culture media. If a large mass of soil is heated and the 

 circulation of the steam is irregular through it then it may be neces- 

 sary to use high temperatures in order to thoroughly impregnate 

 every particle of the soil with steam and thus bring every particle to 

 the same temperature. From a letter which we received from Mr. 

 May we inferred that this was the principal reason for his using high 

 temperatures. Our own experiments upon this point were numerous 

 and they were made with earth containing abundance of nematodes 

 of various species in all stages of development. For the sake of con- 

 venience we will designate these experiments as a-, b, c, etc. In all 

 of these experiments we employed cucumbers in pots of various sizes, 

 (from 4 in. to lo in.), and the plants were left until they were suf- 

 hciently large to show root galls upon them if nematodes were pres- 

 ent in the soil. In every case except "a" the pots containing the 

 infested earth w'ere sterilized in an Arnold steam sterilizer and when 

 moderate heating was required they remained in the sterilizer only a 

 few minutes. The earth in experiment "a" was part of a large lot 

 which was sterilized in a box by means of steam from a boiler. (See 

 lig. II., I, 2, 3). In every instance numerous microscopic examina- 

 tions were made of the soil and roots of the plant in order to deter- 

 ' mine whether nematodes were present. The non-parasitic species 

 are generally present in almost every soil and their presence can 

 very often be suspected by the coloration of the root. They are 

 generally found on the older parts of the root near the surface of the 

 soil as indicated by the dirty brown color of the epidermal tissue. 

 The experiments are as follows : 



Exp. a. Six 4-in. pots were filled with infested earth which had been 

 heated at 212° F. The pots were also sterilized and the cucumber 

 seed after soaking 12 hours in water was placed for 10 minutes in a 

 saturated solution of corrosive sublimate and before using was 

 rinsed with sterilized water. During germination and the growth of 



