440 REPORT OF THE COMMISSIONER OF AGRICULTURE. 



There seems to l)e much difference of opinion with regard to the power 

 of the virus to resist ordinary destructive influences. Under ordinary 

 circumstances, it will be preserved loug-est where it has been dried up 

 and covered from the free access of the air. In close stables and build- 

 ings having rotten wood-work, or deep dust-filled cracks in the masonry, 

 and in those with a closed space beneath a wooden floor, it clings with 

 the greatest tenacity. Again, in buildings which contain piles of lum- 

 ber, litter, hay, fodder, or clothing, the virus is covered up, secreted, 

 and preserved for a much longer period than if left quite empty. In 

 such cases it is preserved as it is in woolen or other textile fabrics when 

 carried from place to place in the clothing of human beings. As carried 

 through the air the distance at which the virus retains its infecting 

 properties varies much with varying conditions. Dr. Law states that 

 he has seen a sick herd separated from a healthy one by not more than 

 fifteen yards and a moderately close board fence of 7 feet high, and in 

 the absence of all intercommunication of attendants, the exposed herd 

 kept i^erfectly sound for six months in succession. x\.t other times in- 

 fection will take place at much greater distances witliout any known 

 means of conveyance on solid objects. Eoll quotes 50 to 100 feet, while 

 others claim to have known infection transmitted a distance of from 200 

 to 300 feet. But the author questions 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. 



Because the lesions are concentrated in the lungs, and begin with 

 cloudiness and swelling of the smaller air tubes and surrounding con- 

 nective tissues, the presumption is favored that the virus is usually 

 taken in with the air breathed. Its progress and the results of all at- 

 tempts at inoculation would seem to confirm this. The exudation into 

 the interlobular tissue, the congestion of the lung tissue itself, and the 

 imi^lication of the lung covering, are regarded as secondary phenomena, 

 or, in other words, the disease begins where the inspired air must lodge 

 the germs. The inoculation of the virulent lung products on distant 

 parts of the body transfers the seat of the disease to the point inocu- 

 lated, and in such cases the lesions of the lungs are not observed, or at 

 least are not greatly marked. 



A diseased animal is more likely to infect a healthy one at that period 

 when the fever runs highest and the lung is being loaded with the mor- 

 bid exudation. Proof appears to be wanting as to the infecting nature 

 of the affection during the incubation stage, but it must not be inferred 

 that with the subsidence of the fever the danger is removed. It is a 

 matter of frequent observation that animals which have passed through 

 the fever, and are again thriving well and giving a free supply of milk, 

 and to ordinary observers appear in perfect health, retain the power of 

 transmitting the disease to others. This may continue for three, six, 

 nine, twelve, or, according to some, even fifteen months after aU signs of 

 acute illness have disappeared. 



The number of animals infected by contact or exposure to the conta- 

 gion is somewhat irregular, as is also the virulenceand fatality of the 

 disease. The French commission of 1849 found that of 20 healthy ani- 

 mals exposed to infection 16 contracted the disease, 10 of them severely. 

 Dr. Lindley gives examples from his South African experience in which 

 whole herds of 80, 130, and even of several hundred died without excep- 

 tion, showing that in warm climates the mortality is greatest. Dr. Law 

 found the disease much more virulent and fatal during the hot summer 

 months in New York, and says that during the winter season it is far 

 less violent in its manifestations, and a great number of animals resist it. 



