10 BULLETIN 819, U. S. DEPARTMENT OF AGRICULTURE. 



Results. 



In no case was the pink yeast recovered from the 20 samples of 

 mud and sand collected. It may be concluded that the soil on the 

 bottom of the bay is not a factor in the contamination of the oysters 

 with the pink yeast. 



A discussion of the distribution of the yeast and its relation to 

 the oyster industry, together with recommendations for its control, 

 is given on page 21. 



EXPERIMENTAL PRODUCTION OF PINK COLOR IN OYSTERS. 



In order to prove conclusively that the pink yeast is the cause of 

 the pink color in shipments of shucked oysters, several experiments 

 were undertaken to produce the color by the introduction of cultures 

 of the organism into jars of normal oysters. 



Two gallons of oysters, obtained in the market, were divided among 

 9 glass jars. Five cubic centimeter amounts of a pink yeast culture, 

 grown in an oyster broth medium for -1 months, were introduced into 

 6 of the jars. The remaining 3 jars were held as controls. Two in- 

 oculated jars and a control jar were placed in the cold storage at 0.5° 

 C, in the refrigerator at from 8 to 10° C, and directly on the ice at 

 about 5° C. These jars were examined daily, the presence or ab- 

 sence of a pink color noted, and the temperature within the jars re- 

 corded. At the end of the first week the oysters in the jars on the 

 ice and in the refrigerator were decidedly pink. There was no pink 

 color in the jars of oysters used as controls. At the end of one 

 month the oysters in the cold storage at 0.5° C. were slightly pink, 

 while the control oysters were not pink. The pink yeast was recov- 

 ered from each jar which showed a pink color. In each jar. how- 

 ever, the oysters were spoiled and very sour by the time they were 

 pink. The oysters used for the experiment were shucked with their 

 own liquor, and were delivered to the laboratory without being 

 washed. They contained a large amount of dirt and many bacteria 

 in the mucus which, without doubt, brought about the rapid spoilage. 



In order to produce the pink color in oysters properly washed 

 and shipped the following experiment was carried out. A trip was 

 made to a near-by city and 3 gallons of oysters purchased at the 

 packing house. These oysters had been carefully shucked and 

 washed in a blower, and then placed in new. clean 1-gallon can-. 

 Into each of two 1-gallon cans of oysters were introduced about 25 

 cc. of a 10-day oyster broth culture of the pink yeast. The third 

 can was left as a control. The cans were closed and packed in a 

 wooden box with cracked ice, and shipped to the laboratory just as 

 they would be shipped to the retailer. These oysters were 5 days in 

 reaching the laboratorv. and when thev were received they were 



