1923] 



DUGGAR & KARRER — NATURE OF MOSAIC DISEASE PARTICLE S 205 



relations, to determine the influence of long-continued grinding 

 under conditions which are generally effective in disrupting 

 living cells. A final series of experiments in this field will be 

 sufficient to indicate the relations encountered. It should be 

 indicated, however, that this series is in accurate accord with 

 less extensive work previously undertaken to determine the same 

 point. The grinding was carried out in an agate mortar with 

 motor-driven, excentrically arranged pestle, the usual device 

 employed in grinding bacterial cultures. Equal amounts by 

 weight of fresh leaf material and diatomaceous earth were used. 



INOCULATION EXPERIMENTS WITH FINELY GROUND MATERIAL 

 FROM DISEASED TOBACCO LEAVES. INTERVAL, 3 WEEKS 



Nature of inoculum 



Ground 3 hours 

 Ground 9 hours 

 Control, no inoculation 

 Control, fresh dis'd. juice 



Total diseased after 4 weeks 

 (ten plants inoculated) 



8 plants diseased 



6 plants diseased 

 None diseased 



7 diseased 



While there has been some inconsistency in the data from other 

 grinding experiments they point in general to one conclusion, 

 namely, that the virus is highly resistant to protracted grinding 

 with diatomaceous earth when the virus is ground with fresh 

 leaf pulp. It is less resistant when filtered through porous cups, 

 then mixed with diatomaceous earth, and ground for 9 hours. 

 The presence of leaf material acts to prevent the greater injury. 

 In order that these experiments may be significant it is necessary 

 to compare the grinding of the tobacco virus with that of a species 

 of bacteria. 



For this purpose also we have employed Bacillus subtilis in 

 the spore condition. Two cc. of a 22-day-old culture in bouillon 

 (rich in spores) were thoroughly mixed with 2 gms. sterile diato- 

 maceous earth in a petri dish. This mixture was then dried, 

 being protected during drying by sterile paper bags. It was then 

 subjected to grinding for the same intervals as previously em- 

 ployed, namely 3, 6, and 9 hours. All possible care was taken to 

 prevent contamination of the material, but some sporadic con- 

 tamination was unavoidable. As the grinding progressed, a sample 



