CHAPTER VII 



CHEMICAL COMPOSITION 



In order to determine the chemical composition of a virus one 

 must be able to isolate and purify adequate amounts of it. Ap- 

 propriate criteria of purity must be applied if the analyses are 

 to have any validity. Therefore, these subjects will be discussed 

 before presentation of the available data on chemical composi- 

 tion. An extensive review, "Bacteriophages," by Putnam 

 (1953) includes methods of concentration and purification, cri- 

 teria of purity, and determination of size, density, and chemical 

 composition of purified bacteriophages. A similar review by 

 Beard (1948), "Purified Animal Viruses," includes some ma- 

 terial on bacteriophages. 



1. Concentration and Purification 



In general, it is unusual to obtain more than 10^" phage par- 

 ticles per ml. in lysates prepared on a large scale. However, 

 lysates of the even-numbered T phages are now easily obtainable 

 which titer up to 5 X 10^^ per ml., or 250 mg. of phage per liter. 

 The first successful purification of phage was achieved by 

 Schlesinger (1933a) using coliphage WLL related to the T2-G16 

 serological group. The host bacteria were grown in a chemi- 

 cally defined medium to avoid contamination of the product 

 with peptones and proteins from the starting material. Bacteria 

 and large particle debris were rem.oved by bacteriological filters. 

 The phage was concentrated by means of collodion membranes 

 of a pore size sufl^ciently small to retain the phage particles. 

 The concentrated phage was further purified by high speed 

 centrifugation. Modern criteria of purity were not yet availa- 

 ble, but comparison of Schlesinger's results with recent data 



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