Jan. IS, 1915 



Moldiness in Butter 



305 



Three slices, one from each of these samples, were put into each one 

 of a series of 24 Petri dishes. The three sUces in each dish were thus 

 under absolutely the same conditions. Six species of mold were then 

 selected and were heavily inoculated into the plated slices— each slice 

 in four Petri dishes being inoculated with one species of mold. Four 

 sets of sLx dishes each were thus available. One set of six Petri dishes 

 was put into a moist chamber (approximately 100 per cent of relative 

 humidity), and one each into the desiccators at 90, 79.6, and 69.6 per 

 cent relative humidity. The cultural results are given in Table III. 



Table HI. — Effects of salt and humidity on mold growth in butter" 



o A typical colony would be designated as i.o; lesser growths by decimal fractions, 

 ft Submerged. 



Examination of this table shows that a single species, Penicillium 

 chrysogenum, was able to produce a colony upon the butter fat plus the 

 water obtainable from the air. Careful examination of the other samples 

 showed no mold. In the low-salted butter, however, with 15.6 per cent 

 of water marked growth occurs; the water in this butter is therefore to be 

 regarded as an essential factor in the molding found here. The butter 

 containing 2.43 per cent of salt shows determinable growth from but two 

 species, P. roqueforti and P. chrysogenum. No growth of species of Alter- 

 naria, Oidium, or Mucor was found upon this butter. The low-salted 

 butter shows very appreciable mold colonies of all species except the 

 Mucor. Growth was greatest in the moist chamber. Nearly as good 

 growth was obtained, however, with a relative humidity of 90.6 per cent, 

 and considerable growth in four of the species with 79.6 per cent. In the 

 presence of 69.6 per cent there was very little visible mold, even in the 

 low-salted sample. The individual samples of low-salted butter all 

 showed the characteristic orange-yellow colors due to the development 

 of spores of Oidium laciis, which were evidently present from the first in 

 all slices. In this experiment the organism grew only in its submerged 

 form; hence, it was little affected by the relative humidity to which the 

 other species responded so clearly. Alternaria and Oidium developed 



