1921] BLAKESLEE, WELCH, & CARTLEDGE—MUCORS 163 
on filter paper above peat moss in shallow galvanized cake tins 
covered with glass plates. The shells of each nut were kept 
separate and placed near the edge of the culture dish in order to 
facilitate their examination with the hand lens. The hands and 
the nut-cracker were sterilized with alcohol after cracking each nut, 
in order to prevent an undue amount of infection of one nut from 
spores which may have been on the one cracked previously. It 
was the usual practice to reserve a culture dish for the nuts obtained 
from a single collection, despite the fact that many of these collec- 
tions were from stores within a radius of thirty-five miles from 
New York City, and very probably had the same ultimate source. 
Another prolific origin of mucors is soil obtained from different 
sources. It was most conveniently scattered on bread, which fur- 
nished a suitable medium for the germination and growth of the 
spores which the soil might happen to contain. The bread before 
using was sterilized in the autoclave without pressure for about 5 
minutes, a longer time not being used since it might make the bread 
soggy. If the surface of the bread has become dry, it may be 
moistened slightly with sterilized water. 
STOCK CULTURES.—The races were obtained in pure cultures 
by making transfers from individual heads in the gross cultures. 
Since there is possibility of spores from another race being on the 
head from which the transfer was made, a second pure transfer 
was regularly made from an individual head in the first test tube, 
thus avoiding the likelihood of the stock cultures being mixtures of 
more than a single strain. As a precaution against too rapid dry- 
ing out, the amount of agar flour in the stock cultures was raised 
from 2 to 3 per cent, and standard no. 230 nutrient, consisting of 2 
per cent each of dextrose and dry malt extract plus o.1 per cent 
meat peptone, was used. 
Inrection.—Knowledge of an investigator’s methods may 
enable the impartial critic to judge whether the known sources of 
experimental error are properly guarded against. To the bacteri- 
ologist and the student of fungi in pure cultures, one of the greatest 
sources of error is infection. When this infection is caused by a 
form different in appearance from the species under cultivation, 
the presence of the foreign cadclesl: is readily recognized. Infection 
