474 REPORT OF THE COMMISSIONER OP AGRICULTURE. 



CAUSES. 



Kothing certain or defiTiite as to tlie causes wliich develop tbe cattle 

 plague are known. In Western Europe it relies solely for its introduc- 

 tion and diffusion to the presence of a contagium, carried eitlier by ani- 

 mals suffering with the disease, those which have been in contact with 

 them, or media of dillVrent kinds which are contaminated with the 

 virus. Once introduced, it spreads from its point of introd action as 

 fi'om a center; each newly-infected animal becomes a focus whence the 

 disease may radiate in every direction, and it usually attacks those ani- 

 mals which are nearest the foci. It spreads with more or less rapid- 

 ity as the animals or vehicles charged with the contagium are moved 

 about ; even the air may, within a certain distance, be credited as an 

 active agent in the diffusion of the deadly malady. The nature of the 

 contagious matter (contagium), has also so far baffled all the efforts 

 of investigators. Neither microscopic examinations nor chemical anal- 

 ysis of the tissues, blood, and mucus discharges of the infected animals, 

 have led to the discovery of the principle of contagion. It is known, 

 however, that from the very beginning of the disease a contagious mat- 

 ter is formed, which attaches itself to every part of the diseased animal. 

 It is principally contained in the secretions of the mucous membranes, 

 but, being volatile, attaches itself also to the urine, the dung, the blood, 

 the skin, and the breath. It may be communicated to the atmosx)here 

 by exhalations from any part of the sick animal, or its carcass. Exi)e- 

 rience has shown that healthy cattle may be infected by coming near 

 the sick animals, or near anything contaminated by then* excrements or 

 exhalations, without actual contact with them. The contagious matter 

 has no eff'ect in open air at a distance of twentj^ to thirty paces, because 

 the air either dilutes or modifies it so as to deprive it of its power. But 

 in cases where a current of air comes directly fi'om an accumulation of in- 

 fected matter, and also in inclosed spaces, the contagion may be carried to 

 greater di stances. Therefore, the disease may be comraunicated in a large 

 stable to a healthy animal quite a long distance from the diseased one, or 

 may be canied from one stable to another as far as a hundred feet apart. 

 This happens only when the exhalations are carried over directly ti'om 

 one stable to the otlier. by a current of air so rapid as not to allow time 

 for the air to dilute or modify the contagious matter. Where one stable 

 is sei')a,rated from another by a partitioii which is not air-tight, the con- 

 tagion is very easily transmitted. Besides these direct means of infec- 

 tion, the disease may be carried to healihy animals indirectly, in many 

 ways. For instance, olyects which have come in contact vnth infected 

 taatter, may be carried to a distant place and there spread the disease. 

 Porous sulystances, such as woolen clothing, wool, hay, straw, &c., are 

 particularly liable to absorb the contagious matter, which may diffuse 

 itself after some time in a distant place. Thus butchers, drovers, and 

 other persons wlio visit infected stables, may carry the disease from yard 

 to yard, and from village to village. In railroad tl^icks, the woodwork 

 absorbs a considerable amount of tihe contagious matter, and, if not 

 thoi^onglily disinfected, may communicate the disease to animals subse- 

 quently placed therein. The dun.g of diseased animals may spread the 

 contag-ion to distant places, by being carried fiway on the wheels of 

 veliicles or the shoes of persons. Bogs and cats may carry it in their fur 

 and birds in tiioir phunage. A small quantity of bloOd or dung on the 

 sole of a shoe or on the tip of a walkirig-stick has sometimes been suffi- 

 cient to carry the disease to a great distance. The modes of possible 

 transmission are, in fact, so nunieroua as to render it, in many instances, 



