268~ DISEASES OF THE DOMESTIC ANIMALS 



inoculated into man from the various animals never causes small- 

 pox, but only the' local lesions seen" in vaccination (vaccinia), and 

 protects -man ' from ' smallpox. Cow-pox, horse-pox and sheep-pb'x v 

 may b'e communicated to man naturally— by contact with 'variolous' 

 animals^bu't, in the case' of sheep-pox, both irioculation' and com- 

 munication by contact are very rare and- 1 difficult to" bring about. 



The fact that the et'iblogical mieroo'rgarii'shi of' variola' (Cyto- 

 ryctes vafiolae) has been discovered in" smallpox, sheep-pox and 

 cow-pox also proves their common origin. This is a protozooh liv-' 

 ing in the epithelial' cells' of the skirt. ! Secondary' irifeetiorf' with 1 

 streptococci accounts for 1 fatal,' pu¥ulehtcaSes\ 



Variola is highly infectious in sheep and is communicated by 

 the secretions, excretions, attendants, infected objects of all kinds, 

 including animals' and insects, and through th^' medium of the air: 



In cow-pox and hofse^pox the ' disease ' appears to' be chiefly' 

 brought about by contact of healthy animals' with variolous " or 1 

 vaccinated persons,' although the disease' may rarely ariSe naturally' 

 in the cow and be transmitted from 'cow to cow by healthy milkers; 



Sheep-pOx is the m'ost 'common, important and fatal. Incuba- 

 tion iS variablc-^fbur to twelve day's! It begins with' conjunctivitis, 

 coryza, and th'e animal ' is feverish, li'es down and ! refuses : food. 

 The eruption appears about the eyes, nose, mouth, inside thighs 

 and arms; and on belly, chest, prepucie, labia; anus and udder, tail/ 

 and often later bec'ornes general'.' It consists first of red papule's on a 

 swollen skin' and these are often surrounded by an areola and have a 

 depressed centre. After a few days the papules become' vesicles, 

 arid- often pustules, and theri 1 yellowish 1 arid b'townish crusts form" 

 which finally drop off, leaving pits and bare spots. The duration 

 is "about one month, and the average mortality io'to 20' per cent., 

 although it may be as high'as 90 per ceiit. The' dangerous fo'rrns' 

 ate the confluent, With' general 'running "together and'su^puratfrig"' 

 eruption, swelling of the head arid eyes, loss' of eyes, : and severe 

 iri'flamiriation' and' gangrene" of the skiri ; ' and' thB hemorrhagic 1 ' 



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