258 ILLINOIS STATE ACADEMY OF SCIENCE 



THE FILTERABLE VIRUSES 



Thomas G. Hull, Ph. D. 



Chief, Division of Laboratories, State Department of 



Public Health, Springfield, Illinois 



There exists just at the range of vision of our most 

 powerful microscopes, or beyond this range of vision, a 

 large number of microorganisms, the identity of which is 

 uncertain. They are called "filterable" viruses because 

 they will pass through our best clay filters. In 1898 the 

 first of these was discovered by Loeffler and Frosch, in 

 studying the foot and mouth disease of cattle. The same 

 year Beijerinck demonstrated as the cause of mosaic di- 

 sease of tobacco, a filterable organism. In passing it is 

 interesting to note that as in bacteriology, where the first 

 diseases studied by Pasteur were in the industries, so in 

 this new class of organisms, initial studies were made up- 

 on diseases of animals and plants. The application to hu- 

 man diseases came later. 



During the next few years, a large number of diseases 

 were investigated in various parts of the world, adding 

 much to our knowledge concerning filterable viruses. By 

 1913, more than forty diseases were attributed to this 

 cause. Among these were diseases of plants, as the mosaic 

 disease of tobacco ; disease of animals, including horses, 

 sheep, cattle, swine, dogs, guinea pigs, rabbits and rats; 

 diseases of birds, especially black birds, and chickens; and 

 diseases of man. The latter list includes small pox, scarlet 

 fever, measles, polyomyelitis, trachoma, rabies, Dengue 

 fever, yellow fever and Rocky Mountain spotted fever. 



Recent literature, especially since the war, has been 

 full of work confirming the filterability of the organisms 

 of these diseases and methods and means of their prophy- 

 laxis. Of more interest, however, are the new diseases of 

 man which are included, namely, influenza, epidemic ence- 

 phalitis, trench fever and the "common cold." There is no 

 need to mention the ravages which influenza has wrought 

 all over the world in the last three years. The discovery 

 of the causative agent is a great step toward its final eradi- 



