910 DISEASES CAUSED BY FILTRABLE VIRUS 



other methods have been elaborated and used to a slight extent. 

 One of the most important of these is the "dilution method" of 

 Hogyes. This method is carried out as follows : A definite quantity 

 of the spinal cord of a rabbit dead of virus fixe is emulsified in 100 

 c.c. of normal salt solution. Dilutions of this emulsion are made 

 and the patient is injected at first with a dilution of 1 -.1,000, subse- 

 quent injections being made of gradually increasing concentration 

 until a concentration of 1 :100 is reached. This method, so far as it 

 has been used, has been satisfactory, but it has not yet found exten- 

 sive application. 



Harris and ShackelP 2 describe an improved method of desic- 

 cating rabic virus which consists in placing the material to be dried 

 in the bottom of a vacuum desiccating jar in the upper part of 

 which is a separate dish containing sulphuric acid. The temperature 

 is reduced by placing the jar in a salt and ice mixture, and after 

 thorough solidification of the material has resulted, a rapid vacuum 

 is produced by a Geryk pump to less than 2 mm. of mercury. The 

 virus so dried will retain its virulence for as long as four months, 

 if guarded against moisture. It will be noted that this method 

 cannot be taken as justifying any particular conclusions as to the 

 nature of the rabic virus since the same method has been applied 

 by Swift and others to the maintenance of the virulence of bacteria. 



Harris 33 believes that the attenuation of a rabic cord in the 

 Pasteur method does not depend primarily upon the loss of water, 

 but rather upon the method of extracting the water. Slow desic- 

 cation attenuates the virus, Harris concludes, by reason of the con- 

 centration of salt and other substances in solution of the brain and 

 cord, the action being thus essentially a chemical one. Harris has 

 studied the minimal lethal dose of his rapidly dried material on 

 animals, and has developed with this material a modified method 

 of immunizing animals and human beings against rabies. 



He prepares suspensions (from the material rapidly dried at 

 zero degrees as above) by emulsifying 10 milligrams in 10 c.c. salt 

 solution. This gives a dilution of 1 milligram to each cubic centi- 

 meter of emulsion, and from this basic suspension dilutions are 

 made. 



32 Harris and Shackell, Jour, of Infec. Dis., 8, 1911, 47. 

 83 Harris, Jour, of Infec. Dis., 13, 1913, 155. 



