Vitality of the Virus. 33 



greatest tenacity. Again, when the buildings contain 

 piles of lumber, litter, hay, fodder or clothing, the virus 

 is covered up, secreted and preserved for a much longer 

 time than if left- quite empty. In these last it is pre- 

 served just as it is in woolen or other textile fabrics and 

 carried from place to place by human beings. 



As carried through the air the distance at which the 

 ■vii'us retains its infecting properties varies much with 

 varying conditions. The author has seen a sick herd 

 separated from a healthy one by not more than fifteen 

 yards and a moderately close board fence of seven feet 

 high, and in the absence of all intercommunication of 

 attendants, the exposed herd kept perfectly sound for six 

 mouths in succession. On the other hand,, infection will 

 sometimes take place at a much greater distance without 

 any known means of conveyance on solid objects. Eioll 

 quotes 50 to 100 feet, while others claim to have seen 

 infection at a distance of 200 and 300 feet. But it may well 

 be questioned whether in such cases the virus had not 

 been dried up on light objects, like feathers, paper, straw 

 or hay, which could be borne on the wind. This, 

 from being in thicker layers, would escape the destruc- 

 tion that would have befallen it had it been carried in 

 the air only as invisible particles. 



How does the Infection enter the System ? 



The seat of the disease, its progress, and the results of 

 aU attempts at inoculation favor the presumption that 

 the virus is usually taken in with the air breathed. Not 

 only are the lesions concentrated in the lungs, but they 

 begin with cloudiness and swelling of the smaller air 

 lubes and surrounding connective tissues. The exuda- 

 tion into the interlobular tissue, the congestion of the 

 lung tissue itself, and the implication o£ the lung cover- 

 ing, are secondary phenomena. In other (vords, the dis- 

 ease begins where the inspired air must lodge the germs. 

 Thus the inoculation of the virulent lung products on dis- 



