1907] JENSEN—TOXIC LIMITS AND STIMULATION 4I 
TABLE XXII 
SUMMATION OF KILLING AND STIMULATING CONCENTRATIONS SELECTED FROM FORE- 
- GOING DATA 
Som CULTURES | SOLUTION CULTURES 
Poison 
Growth inhibited | Growth stimulated | Growth inhibited | Growth stimulated 
" n to On nton on to 25” nto an 
Ni(NO,), tes me A z cs = faa 
1000 10000 100000 10000000 
‘Oo 
ae 30n to Ion 3nton zon to 60on Sinton 
1000 1Ic00o0 IQ0000 
AgNO, am, | 30n to 10H gon to 10” ton to on 20n to 1om 
1000 10000 100000 10000000 
CuSO, eis a 30n to Ion 10on to 4n toom to 50" Nene 
B elerere} 100000 
000n to 2000n 
Fe.(NO;)6 paeat Bc tees AG 40n gon to 30% r1ocon to goon 4 
10000 TOQCC0O 10000000 
Fe,Cl Par sag 40n gon to 20” 1000n to 800n 4000n to 2000” 
WAG 6: 5 aerated Sends —_——— _ —— he a ascot BARS SSNS, Se MES 
1000 10000 100000 10000000 
Pp 50” to 30n gon to 40” 4000n tO 2000” 20000” to 19000” 
TENG oie ind wean Eee Ricci tit shale added a 
T0000 100000 Io0oo0000 
Phenol 20n to Ion 8n to 4n 2000” to 1000n 8000n to 4000n 
sae scree ache 2 ate om <a + aan.” 
Alcohol 750% to 250% 730m to 250% — | ‘7s000" to agcoom | 75000" to 25000" 
ets Se 1000 10000 * 100000 19000000 
tively high position in the toxic table in soil should occupy the same 
relative position in solution cultures. Hence the assumption upon 
Which Harter (18) worked is not verified by my results. 
The reduction of toxic effect (seen by comparing columns 1 and 
3, Table XXII) is most marked in Ni, less in Ag, Zn, Cu, Fe, and 
Pb, in the order given, and no reduction whatever is apparent in 
phenol or alcohol. 
Stimulation to growth takes place more markedly in soil than in 
solution, because in soil every test gave accelerating effects, while in 
Solution cultures two failed to give such results. Stimulation in 
soil is always at a much higher concentration than stimulation in 
solution except in the case of the organic poisons tried, phenol and 
alcohol, where the presence of quartz does not reduce the toxicity. 
Conclusions 
In conclusion I wish to point out what seem to me the most salient 
features of this research. 
1. While considerable work has been done on toxicity, none 
has shown the definite effects of a poison in pure soil, for, as I have 
