630 KUNKEL: INFLUENCE OF STARCH, PEPTONE, AND SUGARS ON 
Zinc nitrate in starch media is far more toxic than any of the 
other nitrates used; at a concentration of 0.000034 molar, it 
inhibited the germination of spores. In a concentration of 
0.000025 molar, the spores germinated and produced microscopic 
mycelia, but when the zinc nitrate was used at a concentration 
of 0.000017 molar or less, abundant growth was obtained. 
Ammonium tartrate is the only organic salt that was tried in 
these experiments. In starch media it is slightly more toxic than 
ammonium nitrate. Ina concentration of 0.025 molar, the spores 
germinated but produced only microscopic mycelia, while in a 
like medium containing the same concentration of ammonium 
nitrate abundant growth was obtained. 
As shown by TABLE I zinc nitrate is the most toxic substance 
used in starch media. If its limit concentration be taken as one 
then the limit concentrations of the other nitrates in the same 
medium may be expressed, by comparing equimolecular con- 
centrations, approximately by the following numbers: silver 
nitrate, 5; ferric nitrate, 26; aluminum nitrate, 52; ammonium 
nitrate, 1,520; urea nitrate, 1,600; calcium nitrate, 16,560; and 
potassium nitrate, 53,200. 
To show at a glance the relative toxic values of the various 
substances used, they are given in the order of their toxicity in 
TABLE II. That toxicity does not seem to be related io the 
valence of the kation is also shown by this table. 
TABLE II 
THE RELATIVE TOXICITY OF VARIOUS SALTS IN STARCH MEDIA 
Valence of kation Toxic concentration 
Monovalent.......... 133 molar potassium nitrate 
oh. Re Eee ree 464 : calcium - 
Monovalent.......... 400 = sodium ch 
age pee ies 156 “ barium 
Monovalent.......... 040 : urea $3 
Monovalent.......... 038 " monium * 
onovalent.;.. 0... 025 . ammonium tartrate 
Trivadlents oon As 0013 in aluminum nitrate 
eat eR ASS 00067“ ferric z 
Monovalent.......... 00013 ** silver m8 
Divelentcc0 ok: 000025“ zine ef 
The table shows, in the case of each salt, the greatest com 
centration at which growth was obtained when the salt was used 
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