AVERY, MACLEOD, MCCARTY 



sho\\'ed maxima in the region of 2600 

 A and minima in the region of 2350 

 A. These findings are characteristic of 

 nucleic acids. 



Quantitative Detemmiation of Bio- 

 logical Activity.— In its highly purified 

 state the material as isolated has been 

 found to be capable of inducing trans- 



187 



formation in amounts ranging from 

 0.02 to 0.003/xg. Preparation 44, the 

 purification of which was carried out 

 at low temperature and which had a 

 nitrogen-phosphorus ratio of 1.58, ex- 

 hibited high transforming activity. Ti- 

 tration of the activity of this prepara- 

 tion is given in Table IV. 



Table IV 



Titration of Transfomiing Acitivity of Preparation 44 



* Solution from which dilutions were made contained 0.5 mg. per cc. of purified material. 

 0.2 cc. of each dilution added to quadruplicate tubes containing 2.0 cc. of standard serum 

 broth. 0.05 cc. of a 10 — ^ dilution of a blood broth culture of R36A is added to each tube. 



A solution containing 0.5 mg. per 

 cc. was serially diluted as shown in the 

 protocol. 0.2 cc. of each of these dilu- 

 tions was added to quadruplicate tubes 

 containing 2.0 cc. of standard serum 

 broth. All tubes were then inoculated 

 with 0.05 cc. of a 10~^ dilution of a 5 

 to 8 hour blood broth culture of 

 R36A. Transforming activity was de- 

 termined by the procedure described 

 under A^ethod of titration. 



The data presented in Table IV 

 show that on the basis of dry weight 

 0.003 iUg. of the active material brought 

 about transformation. Since the reac- 

 tion system containing the 0.003 /xg. 

 has a volume of 2.25 cc, this represents 

 a final concentration of the purified 

 substance of 1 part in 600,000,000. 



DISCUSSION 



The present study deals with the re- 

 sults of an attempt to determine the 

 chemical nature of the substance in- 

 ducing specific transformation of 

 pneumococcal types. A desoxyribo- 

 nucleic acid fraction has been isolated 

 from Type III pneumococci which is 

 capable of transforming unencap- 

 sulated R variants derived from Pneu- 

 mococcus Type II into fully encap- 

 sulated Type III cells. Thompson and 

 Dubos (21) have isolated from pneu- 

 mococci a nucleic acid of the ribose 

 type. So far as the writers are aware, 

 however, a nucleic acid of the desoxy- 

 ribose type has not heretofore been 

 recovered from pneumococci nor has 



