Bacterial Viruses in the Sea 357 



exposure at 45 C, and in only one case, P/14, at 50 C. With 

 phages P/L/34, P/SWl/a, F/SWi/Z?, and P/SW3i, inactivation 

 became evident after an hour's exposure at 55 C and was virtually 

 complete within five minutes at 65 C. Phage P/SW38, however, 

 showed no signs of inactivation after one hour's exposure at 65 C. 



The resistance to thermal inactivation of tlie least resistant 

 phage, P/14, was investigated in more detail. Samples of the 

 stock preparation were diluted ten-fold in sea water peptone 

 water or other media, and standard drops of these preparations 

 were placed by means of a dropping pipette onto a waxed sur- 

 face. These drops were then taken up by capillarity in fine 

 capillary tubes. The lower ends of the tubes were heat sealed 

 and the tubes placed in water baths at various temperatiues. 

 Tubes were withdrawm after various periods of time and the 

 contents expelled into 1 ml amounts of sea water broth at room 

 temperature, 20-22 C. Plaque counts were then made on these 

 samples. Figure 1 shows the progress of thermal inactivation at 

 40, 45 and 50 C of P/14 in sea water peptone water and it is 

 evident that considerable thermal inactivation was taking place 

 at 45 C although it was not detectable by the previous cruder 

 method. A similar slight degree of inactivation at 40 C to that in 

 sea water peptone water also took place in sea water broth while 

 inactivation in tap water broth or peptone water was slightly more 

 rapid. Although this point has not yet been examined, it is proba- 

 ble that a more detailed examination of the other phages by this 

 method would similarly show thermal inactivation at somewhat 

 lower temperature than shown in Table 3. 



The hterature on the thermal inactivation of phages can not 

 be reviewed here but it would appear that, in general, terrestrial 

 phages suspended in organic media such as broth are not appre- 

 ciably inactivated within one hour at temperatures below 60 C. 

 Five of the six marine phages, however, showed complete or 

 marked inactivation within one hour at 55 C and were probably 

 undergoing inactivation at 50 C, certainly so in the case of P/14, 

 and it would thus appear that the marine phages examined are, 

 in general, more heat sensitive than terrestrial bacteriophages. 

 Phage P/SW38 may, however, possess the more extreme degree 

 of thermal stabihty exhibited by many of the phages active 



