THOMAS M. RIVERS 519 



bacterial diseases. Oroya fever and fowl diphtheria, in view of Noguchi's' work and 

 Bordet's^ experiments, respectively, do not belong here. Enough has been said to 

 convince one of the heterogeneity of the diseases listed in the table. In fact, they ex- 

 hibit so many differences that a discussion of the filterable viruses almost amounts to 

 a separate discussion of each disease. Such a state of affairs is due to the fact that the 

 filterable virus group has been used to a considerable extent for the indiscriminate 

 segregation of infectious diseases of unknown etiology. Therefore, it is not unlikely 

 that some of them will be shown to be caused by small bacteria or protozoa. When 

 this occurs, such diseases should be removed from the filterable virus group and 

 given their correct position in the classification of diseases. 



riLTER.'VBILITY AND SIZE OF VIRUSES 



By means of different kinds of filters it has been determined that many diseases 

 are caused by active agents supposedly smaller than ordinary bacteria. Some of them 

 are presumably much smaller and are most likely optically immeasurable. Others, 

 however, do not seem to be so small, and concerning their filterability there is much 

 discussion. Methods of filtration are crude and inaccurate, and the most one can say 

 concerning the viruses is that under given experimental conditions they either pass or 

 do not pass through certain filters. The failure to pass through a filter, however, is 

 certainly not determined in every instance by the size of the virus. The electrical 

 charge on the virus, the electrical charge on the filter, the adsorption of the virus by 

 aggregates of protein or by cell detritus, the amount of protein or other substances in 

 the virus emulsion, the temperature at which the filtration is conducted, the'amount 

 of negative or positive pressure employed, the duration of filtration, and other factors 

 not mentioned or not known serve to influence the results of all filtration experiments. 

 Furthermore, sufficient attention has not been given to the possibility that some filters 

 may not only hold back certain viruses but may also inactivate them in some manner 

 so that they can never become active again. ^ 



Very Httle has been recorded in regard to the size of many of the viruses other 

 than that they pass through certain kinds of filters. It is obvious that this method 

 indicates only roughly that the viruses which pass through tight Chamberland candles 

 are very small. No virus has been obtained in an absolutely pure state. Therefore, it 

 is impossible to say that virus alone is being filtered rather than virus attached to ag- 

 gregates of protein or particles of degraded cells. Nevertheless, attempts have been 

 made in various ways to determine the size of a few viruses. According to D'Herelle,'' 

 the diameter of the bacteriophage is 20-30 mm- Bechhold and Villa-^ state that its 

 diameter is more than 35 and less than 200 ii^x. Duggar and Karrer*" believe that the 



' Noguchi, H., and Battistini, T. S.: /. Exper. Med., 43, 851. 1926; Noguchi, H.: ibid., 44, 533. 

 1926; 45, 175. 1927. 



- Bordet, J.: Bidl. Soc. sc. med. cl nat., 65, 125. Bruxelles, 1Q07; 67, 196. 1909; Ccntralbl. f. 

 Bakkriol., Abt. I, Orig., 67, 41. 1913. 



3 Coplans, M.: /. Trop. Med., 29, 122, 133. 1926. 



"d'Herelle, F.: Centralbl. f. BakterioL, Abt. I, Orig., 96, 385. 1925. 



5 Bechhold, H., and Villa, L.: Biochcm. Ztschr., 165, 250. 1925; Centralbl. f. BakterioL, Abt. I, 

 Orig-, 97.* 162. 1926; Ztschr. f. Hyg. u. Infektionskrankh., 105, 601. 1926. 



" Duggar, B. M., and Karrer, J. L.: Ann. Missouri Bot. Card., 8, 343. 1921. 



