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IOWA ACADEMY OF SCIENCES. 
pigment is dependent on the presence of air. On gelatin 
the colonies are small and rose-colored, afterwards deepen- 
ing in hue; the medium is not liquefied.” 
The black spots so often found on Parmesan cheese, and 
that so often give forth the odor of garlic, are caused by 
bacteria. Herr G. Marpmann indicates that these 
black spots are due to the presence of ferrophilous bacteria 
that form sulphides. The pigment is produced only when 
the media contains iron. The presence of iron and sul- 
phides is easily demonstrable by the ordinary chemical 
tests. The garlicky odor is common to decomposing 
organic matter w^hich contains phosphates, and is due to^ 
the presence of phosphuretted hydrogen. The presence of 
this compound can be demonstrated, and distinguished 
from sulphuretted hydrogen by the reaction to test-papers 
moistened with silver nitrate and lead acetate solutions. 
The former is stained by the phosphuretted hydrogen, the 
latter by the sulphur compound.” 
The B. violaceiis produces purple color that is quite as 
characteristic as the red, blue and green pigments, but in 
standard books on bacteriology little seems to have been 
written abaut it. How^ever, about 1895 Prof. H. M. 
Ward describes a violet bacillus which was derived from 
the Thames. “Morphologically it presents itself in the 
form of rodlets or filaments. These rodlets may be so 
short as to be almost cocci. It may be quiescent or actively 
motile, and in old cultures involution forms are found. 
Spore formation was not observed. It is aerobic, liquefies 
gelatin, grows slowly, its optimum temperature is 20°, it 
is easily killed by direct sunlight, and is not pathogenic to 
animals. It was grown on gelatin, agar, potato, or broth 
and milk. The growth at first white, develops later a 
violet pigment which is insoluble in water, but very, 
soluble in alcohol. It is very stable, except in sunlight, 
is turned bluish-green on adding caustic alkali, the color 
nearly returning by excess of acid.” Many of the North 
American chromogenic bacteria have been treated by other 
writers, such as Sternberg, and Jordan. Miss Hef- 
