520 FILTERABLE VIRUSES 



\nrus of tobacco mosaic is approximately the same size as the colloidal particles of 

 fresh I per cent hemoglobin (30 fx/x). 



The size and weight of molecules of crystalline egg albumen and crystalline hemo- 

 globin are not agreed upon. Bechhold' states that an aggregate of 50 molecules of egg 

 albumen is greater than 4 and less than 10 fx/j. in diameter. According to Du Noiiy,- 

 however, i molecule of egg albumen is 4.1 /x/x in diameter. If it is difficult to deter- 

 mine the size of molecules of relatively pure crystalline substances, what hope is there 

 at present of ascertaining the size of the viruses which have not been obtained in a 

 pure state? Furthermore, it is useless to pretend to know what is the lower limit in 

 point of size for living things. In general, however, it can be said that many viruses 

 are probably of sufficient size to exist in a living state, and that others are probably 

 small enough to satisfy the demands of those who insist that they are not possessed of 

 life. 



VIABILITY OF VIRUSES 



The question as to whether the viruses are animate or inanimate is also an old one, 

 inasmuch as it was propounded simultaneously with the discovery of the filterability 

 of these agents. Beijerinck's^ idea of a living contagious fluid called forth many pro- 

 tests. Sanfelice,^ working with fowl-pox in 1914, was led to think of it as an inanimate 

 poison capable of attacking normal cells and producing within them a poison of a sim- 

 ilar nature which in turn could attack other normal cells. Thus he described his idea 

 of how a lifeless agent might be passed in series, reproducing itself indefinitely. The 

 work of Twort, D'Herelle, Bordet, and others, concerning the bacteriophage, is fa- 

 miliar to all. The numerous discussions concerning the nature of this active agent 

 have led many investigators to question more closely the Hving nature of other filter- 

 able viruses. 5 Many tests have been devised to act as criteria for the presence of life 

 but so far no one of them has been found satisfactory. Therefore, it is impossible at 

 present to say whether the viruses are animate or inanimate. Furthermore, it is wise 

 to leave the subject at this point as a further pursuit of it leads one into the sterile 

 discussion of what life is — a problem still in the realm of metaphysics. 



VARIATIONS or VIRUSES 



Mutations of bacteria with concomitant changes in their characteristics are at 

 present of particular interest to bacteriologists. The question arises, then, as to 

 whether viruses can mutate. In the field of filterable viruses, however, this is not a 

 new question inasmuch as it has been under discussion in regard to the relation be- 

 tween vaccine virus and the virus of smallpox since Jenner's time. In spite of all con- 

 tradictions, it seems that smallpox virus passed through calves for several generations 

 becomes vaccine virus. '^ Furthermore, if a sufficient number of passages is made in 

 calves, it is impossible for this altered virus to regain the characteristics of smallpox 



'Bechhokl, H., and Villa, L.: loc. cU. 



- du Noiiy, P. L.: Surface Equilibria of Biological and Organic Colloids. New York: Chcm. Cat. 

 Co. ("Am. Chem. Soc. Mono. Series"), 1926. 



3Beijerinck, M. W.: Centralhl. f. Bahteri-.^l., Abt. II, 5, 27, 310. 1S99. 



^Sanfelice, F.: Zlsclir. f. //v.i;. u. Infcklionskrankli., 76, 257. 1914. 



5 Simon, C. K.: Physiol. Rev., 3, 4S3. 1923. 



•■Copeman, S. M.: J. Path. cT Bad., 2, 407. 1S94; Proc. Roy. Soc, London, 71, 121. 1903. 



