3o6 Journal of Agricultural Research voi. iii.no.4 



only in the low-salted samples. Alternaria appeared in several places 

 without inoculation. Rhizopus nigricans was found once in a moist- 

 chamber sample. Aspergillus fumigatus and A. nigcr both appeared 

 in one or more cases, but none of these species appeared where the per- 

 centage of salt was 2.43. 



The same fact is illustrated on a larger scale by the tub of butter 

 analyzed as No. 3546 in Table I. Of the three samples packed together 

 in one tub the middle layer was low-salted and typically moldy, while 

 the top and bottom layers were free from mold. 



These results harmonize fully with the data from the analysis of butter 

 as found in Table I and with the preliminary cultural data as given in 

 subsequent experiments. Two of the three types of moldiness, the 

 smudged and the orange-yellow forms, occur only in butter containing 

 less than 2 per cent of salt. Even with green molds under high humi- 

 dities and at temperatures far above those used in storage, growth in 

 these experiments was negligible in butter with a salt content of 2.43 

 per cent. 



THE SALT FACTOR IN MOLD GROWTH 



The salt factor in butter is calculated as follows: Thompson, Shaw, 

 and Norton (191 2), in analyzing 695 samples of American creamery but- 

 ter, found an average water content of 13.9 per cent; salt content, 2.51 

 per cent; and curd content, 1.18 per cent. This amount of salt in solu- 

 tion in the water present forms, therefore, approximately a 13 per cent 

 brine, which represents the brine formed by adding 18 parts of salt to 

 100 parts of water. If the same water content be assumed and the 

 salt content found be i per cent, the brine present is 5.1 per cent (made 

 by adding 7.1 parts of salt to 100 parts of water) ; with a salt content of 

 2 per cent, this strength would be 10.2 per cent; with 3, 15.3 per cent; 

 and with 4, 20.4 per cent. For purposes of mold growth the strength 

 of the brine found is one very significant factor. Another factor is repre- 

 sented by the distribution of air and moisture throughout the mass of 

 butter, and still a third by the relative humidities to which the butter 

 is subjected. 



To obtain more complete cultural data for comparison, a series of 

 cultures was made with media containing known percentages of salt. 

 For this purpose 6.5 per cent of salt was introduced into one lot of 

 Czapek's agar (Dox, 1910) and 14 per cent in a second lot. The first 

 represents approximately the proportion of brine in butter with 1.3 

 per cent of salt, the second the brine with a content of about 2.8 per 

 cent of salt. These cultures were grown in a moist chamber to eliminate 

 the concentration of the brine by drying. The cultural results are given 

 in Table IV. 



