FUNGI IN CHEESE RIPENING. aT 
studies of species of such a genus as Penicillium their value is 
only that of a useful accessory. ‘The primary source of com- 
parative data must be direct study of the growing colony undis- 
turbed upon the culture medium, with the best lenses that 
admit of such use. 
This method of study recognizes that morphology is the 
basis of fungus determination, but takes into consideration : 
1. That morphology must not only include the minutest 
details of cell structure and cell relations such as are undis- 
turbed in fluid mounts, but also the appearance and character 
of the colony. 
2. That the morphology of the colony—~z. e. the size of con- 
idiophore and fructification, relation of these to substratum, 
appearances and relations of aerial and submerged mycelium— 
is different upon various substrata, but has been found to be 
characteristic for each particular substratum. 
3. That a description of morphology to be of value must 
therefore, specify the formula of the medium used and the 
conditions. 
Dilution cultures have been necessary usually to obtain the 
colonies pure, but the direct transfer of large numbers of spores 
upon a platinum needle to the surface of gelatine or agar plates 
which have been allowed to cool have been found to give 
equally reliable results and to have many advantages for the 
study of species once obtained in pure culture. This is often 
spoken of as inoculation of cold poured plates. Litmus solu- 
tion may be used with either gelatine or agar and gives striking 
evidence of differences in, and in the rate of the physiological 
action of different species. Bacterial contamination has been 
usually restrained by the addition of from two to four drops of 
normal lactic acid to eight or ten cubic centimeters. 
EFFECT OF A FUNGUS UPON A CULTURE MEDIUM. 
In studying the relation of a fungus to a culture medium 
we find (1) that the fungus absorbs food from the surrounding 
medium; (2) that it may secrete or excrete substances into 
the medium which may transform its chemical composition and 
its appearance. The amount of food absorbed by the fungus 
