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



the box, and the yeast which was dried on it washed off in dextrose 

 broth. As each rod was taken from the box the hole was plugged 

 with a sterile cotton plug. The tubes of broth in which the dried 

 rods were washed were incubated at room temperature, and observed 

 for the growth of the yeast. 



Up to July 1, 1918, the yeast was recovered in pure culture from 

 rods suspended in the drying-box for 100 days. The fact that dry- 

 ing under atmospheric conditions apparently has no effect on the 

 viability of the pink yeast helps to explain why the yeast, after be- 

 ing dried in oyster bins, etc., for several months, will readily grow 

 when placed in a favorable environment. 



RESISTANCE OF THE PINK YEAST TO DISINFECTANTS. 



Early in the study of the pink yeast an attempt was made to find 

 a disinfectant with which the infected objects in the oyster house 

 could be washed as a method of controlling the development of the 

 yeast. It was necessar}^ to use a chemical which would in no way 

 be injurious to the oysters should it come in contact with them, or 

 harmful to the consumer in case such oysters were eaten. 



Chemicals employed in the disinfection of water, such as calcium 

 hypochlorite, or bleaching powder, and copper sulphate, were first 

 used. Neither of these proved efficient in dilutions such as it was 

 feasible to use. Since the yeast was known to be surrounded by a 

 capsule, probably of a lipoid nature, soap and soapine solutions were 

 tried, in the hope of breaking the capsule and thus killing the yeast. 

 When this failed, copper sulphate was mixed with the soap solution 

 in the belief that the soap might break the capsule and allow the 

 copper sulphate to act. This treatment, however, had no effect on 

 the viability of the yeast. A coal-tar disinfectant in a dilution of 

 1 to 1,000 parts was not effective, and sodium sulphite and copperas 

 in low dilution were also found to be without effect. Formalin, 

 which was not used at first because of its odor and the fact that 

 molds often grow readily on it, was finally resorted to. It was 

 found that formaldehyde gas present in 1 to 2,500 parts of water 

 quickly kills the yeast. 



In testing the effects of disinfectants on the yeast, the following 

 method was employed : The yeast was grown in 9 cc. amounts of 

 dextrose broth for from three to five days. The disinfectant to be 

 tested was diluted in such a manner that 1 cc. added to the 9 cc. of 

 culture would give the required dilution. In the case of calcium 

 hypochlorite the amount of available chlorin was first determined, 

 and dilutions prepared which contained known amounts of the 

 chlorin. When testing formalin, dilutions were made from the com- 

 mercial 40 per cent solution, and the amount of formaldehyde gas 

 in the final dilution was computed. The cultures to which the dis- 

 infectant had been added were set aside for known lengths of time ; 



