OSWALD T. AVERY, COLIN M. MACLEOD, AND MACLYN MCCARTY 



145 



for desoxyribonucleic acid is strongly positive. The orcinol test (Bial) for 

 ribonucleic acid is weakly positive. However, it has been found that in similar 

 concentrations pure preparations of desoxyribonucleic acid of animal origin 

 prepared by different methods give a Bial reaction of corresponding intensity. 



Although no specific tests for the presence of lipid in the purified material 

 have been made, it has been found that crude material can be repeatedly ex- 

 tracted with alcohol and ether at — 12°C. without loss of activity. In addition, 

 as will be noted in the preparative procedures, repeated alcohol precipitation 

 and treatment with chloroform result in no decrease in biological activity. 



Elementary Chemical Analysis. 1 — Four purified preparations were analyzed 

 for content of nitrogen, phosphorus, carbon, and hydrogen. The results are 

 presented in Table I. The nitrogen-phosphorus ratios vary from 1.58 to 1.75 

 with an average value of 1.67 which is in close agreement with that calculated 



TABLE I 



Elementary Chemical Analysis of Purified Preparations of the Transforming Substance. 



on the basis of the theoretical structure of sodium 'desoxyribonucleate (tetra- 

 nucleotide). The analytical figures by themselves do not establish that the 

 substance isolated is a pure chemical entity. However, on the basis of the 

 nitrogen-phosphorus ratio, it would appear that little protein or other sub- 

 stances containing nitrogen or phosphorus are present as impurities since if 

 they were this ratio would be considerably altered. 



Enzymatic Analysis. — Various crude and crystalline enzymes 2 have been 

 tested for their capacity to destroy the biological activity of potent bacterial 

 extracts. Extracts buffered at the optimal pH, to which were added crystalline 

 trypsin and chymotrypsin or combinations of both, suffered no loss in activity 

 following treatment with these enzymes. Pepsin could not be tested because 



1 The elementary chemical analyses were made by Dr. A. Elek of The Rockefeller 

 Institute. 



2 The authors are indebted to Dr. lohn H. Northrop and Dr. M. Kunitz of The 

 Rockefeller Institute for Medical Research, Princeton, N. J., for the samples of 

 crystalline trypsin, chymotrypsin, and ribonuclease used in this work. 



'95 



