DISEASES OP THE OX AND SHEEP. 305 



which have been produced by various non-infective inflammations. 

 It is therefore manifest that, in order to make sure that they are 

 the active cause of the disease, it would be necessary to cultivate 

 them for several generations, and with the latest-formed micro- 

 cocci to inoculate other animals, and then, if the disease makes 

 its appearance in these animals experimented upon, the proof 

 that the micrococci are the exciting cause of the malady would 

 be complete. 



The virus of variola retains its noxious powers for a very long 

 period. The symptoms of this malady are acute, febrile, and 

 regular. Betwixt the time of the reception of the virus and the 

 appearance of febrile symptoms, a period of incubation intervenes. 

 If the disease has been produced by means of inoculation, this 

 latent stage lasts about seven days and a half; but if it has been 

 acquired by ordinary natural means, about twelve days and a half 

 elapse before the malady expresses itself. 



Small-pox (or Variola) of Man. 

 Small-pox is a specific lever spreading by infection and 

 contagion, and especially characterised by the appearance on the 

 third day of a papular eruption which gradually becomes 

 pustular, and attains its full development on about the eleventh 

 day of the disease. The eruption is also shown in the mucous 

 membrane of the mouth, fauces, and larynx. 



At about the close of the eighteenth century, Jenner's dis- 

 covery was made, and since then small-pox has not been so 

 larkedly fatal. Instances are not at all uncommon in which 

 )ersons have a second or even a third attack ; but such attacks 

 re generally mild. People who have not been attacked for 

 lany years, although exposed to contagion, may at last contract 

 the disease in a severe form. 



Supposing it to have arisen by inoculation, on the second day a 

 small papule shows itself at the seat of puncture, and by the fourth 

 day this is converted into an umbilicated vesicle. On the seventh 

 day the vesicle has become a pustule, and the lymphatic glands 

 are swollen and tender. On this day, or the following day, rigors 

 and other symptoms occur. About the tenth or eleventh day 

 the pustule is fully developed, and the general variolous rash 

 occurs. By the fourteenth day the pustule has dried up into a 

 scab. The usual period of incubation, when the disease is 



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