VITAMINES AND GROWTH OF STREPTOCOCCUS 459 



selected. ]\Iuch to our suri)ii.sc the same stimulation of growth 

 of the streptococcus occurred as with butterfat and cod-liver oil. 



In these prelininary experiments there was no accurate measure 

 of the degree of stimulation of growth, for it had been judged 

 only b\' the appearance of the turbidity of the cultures after shak- 

 ing. A more accurate measure was desired and the following 

 method was adopted. Flasks containing 50 cc. of the yeast 

 peptone medium with 1 per cent of a number of different oils- 

 were inoculated with a loopful of a water suspension of a twenty- 

 four-hour growth of the streptococcus on agar. After twenty- 

 four hours' incubation at 37°C. the amount of growth was deter- 

 mined bj' plating on infusion agar. The results of these experi- 

 ments are shown in table 3. It will be seen that the inoculated 

 control peptone yeast medium without oil contained 170,000 

 bacteria per cubic centimeter after twentj^-four hours of incuba- 

 tion. With sesame oil there was apparently little if any stimula- 

 tion, while chaubnoogra oil seemed to be toxic. The rest of 

 the oils and fats increased the count to a considerable degree. 

 Some of the vegetable oils were considerably active, as for 

 example okra-seed oil. This result is based on only one experi- 

 ment, and in a repetition of the experiment a count was 

 obtained with okra-seed oil similar to those observed with the 

 other oils. 



The most interesting feature of the results was the marked 

 stimulation of growth by mineral oil, vaseline, and even solid 

 paraffin. Microscopic examinations were made in some cases 

 to prove that the plate count represented a difference in the 

 actual number of cells in the cultures. Since we were working 

 with a chain-forming streptococcus, the influence of the oil might 

 have been to decrease chain formation, and therefore apparently 

 increase the count. Microscopic tests showed, however, that 

 the plate count represented the real difference in growth. 



The results so far were obtained in media containing 1 per 

 cent of the various oils but it was thought that this percentage 

 could be lowered. To this end oils were selected from the three 



' We are indebted to Doctor Jameison of the Bureau of Chemistry for many 

 of the oils used in our experiments. 



