BIOLOGICAL ROLE OF DEOXYPENTOSE NUCLEIC ACIDS 473 



IV. Summary — Infection, Heredity, and Infectious Heredity 



The deoxypentose nucleic acids are significant participants in those mech- 

 anisms whereby the various forms of Hving matter pass on to their progeny 

 their various specifically organized patterns of growth and metabolism. 

 These substances are prominent constituents of the nuclei of perhaps all 

 cells. Upon some species of bacteria, specific deoxypentose nucleic acids can 

 act even in isolated form as genetic determinants. Their diversity of chem- 

 ical composition and especially of organization is sufficient to allow for 

 their functioning in countless different specific genetic roles. Furthermore, 

 as cell constituents of remarkable metabolic stability, the deoxypentose 

 nucleic acids are found to increase in amount in close relation to growth. 

 The behavior of this component in cells of the higher forms is organized 

 with nice precision at the successive levels of the nucleus, the chromosome, 

 the linkage group, and the gene. Among the lower orders, the growth of 

 the more exacting parasitic forms involves formation of parasite deoxy- 

 pentose nucleate more or less directly at the expense of this component of 

 the host cell, and is called an infection. In the case of certain bacterial 

 viruses, such an infection clearly partakes of the nature of an intimate 

 reorganization of the host's genetic mechanisms, induced by deoxypentose- 

 nucleate particles. At this point, the simplest infective processes become 

 analogous to the simplest genetic processes, the bacterial transformations. 

 Both furnish indications that the native deoxypentose nucleate-containing 

 particle is a fundamental biological unit capable of initiating a process 

 which can be viewed under some circumstances as genetic, or under others 

 as infectious. 



