560 Sir John Rose Bradford [May 30, 



as they are liable to fade. The organisms are Gram-positive in 

 young cultures, but old cultures also contain many Gram-negative 

 specimens. 



All these six organisms are filter-passers in the usual sense 

 attached to the term ; they pass through certain filters, e.g. Berkefeld 

 N & Y, and through most Massen filters. Some of them, e.g. the 

 polyneuritis organism, do not pass through the finest Massen filters ; 

 but the smallest, like those of rabies and influenza, pass through the 

 finest Massen filters obtainable. In the case of the more porous 

 Berkefeld filter, half-an-hour to an hour is required ; with the 

 Massen porcelain filter as much as three to four hours are necessary. 

 It will suffice to say here that in all such experiments the filters are 

 carefully cleaned, washed, sterilised and tested as to their permea- 

 bility with fluids containing known organisms of known size. Finally, 

 a negative pressure of something less than one atmosphere was used 

 as an aspirating force. 



Another point of general interest with regard to these viruses is 

 their resistance, i.e. the facility or otherwise with which they are 

 killed. It has long been known that the virus of certain diseases was 

 extraordinarily resistant and remained potent for long periods. Thus 

 the old physicians, who were shrewd observers, drew attention to the 

 fact that the unknown poison of scarlet fever could remain dormant 

 but potent for many years, and that scarlet fever had occurred as a 

 result of wearing clothes that had formerly been worn by one 

 who had died of scarlet fever, the garments then put away and 

 the facts forgotten. In more recent times the virus of several 

 diseases — e.g. horse sickness, rabies— has been proved in the labora- 

 tory to be very resistant to the action of antiseptics even when 

 in contact with them, in some cases for months. Still more recently 

 the American observers showed that the virus of poliomyelitis might 

 remain potent for several years when kept in glycerine. The resist- 

 ance of these viruses to the action of glycerine, which is very 

 destructive to the more conmion bacteria, is a fact of the first 

 importance, as it is partly owing to this property that it has been 

 possible to grow these organisms from the blood and tissues. The 

 resistance to glycerine varies in degree in different cases. Thus the 

 viruses of polyneuritis, encephalitis and rabies are resistant for pro- 

 longed periods ; in the case of polyneuritis and of encephalitis this 

 may extend to many months. In the case of rabies it is not so 

 ])rolonged, and with trench fever it is approximately three months. 

 In influenza and nephritis the duration is much shorter, only a few 

 weeks. The long duration of virulence in the case of the globoids 

 is certainly a most remarkable fact, as cultures can be obtained from 

 nerve tissue kept in 50 per cent glycerine for as long as twelve 

 months, and the disease can also be reproduced in animals by suitable 

 inoculation with such glycerinised material. 



These viruses in culture are resistant to heat — e.g. to a tempera- 



