COW-POX — VACCINIA. 667 



When cow-pox is accidental or the result of inoculation, the eruption 

 occurs exactly at the point of inoculation, whether the latter has been 

 through an abrasion, a puncture, an incision, or any other skin injury, 

 and the eruption may assume the most varied appearances, according 

 to the nature of the primary lesion, although the mode in which the 

 pustules themselves form never varies. Pustules experimentally pro- 

 duced by puncturing the parts may be taken as a type of inoculation. 

 On the day following the operation nothing abnormal appears. On 

 the third day there is a slight swelling around the point punctured, 

 and this increases until the fifth day, when there is exudation, which 

 converts the primary lesion into a vesico-pustule. On the sixth day 

 the vesico-pustule becomes umbilicated at its centre, the exudation is 

 abundant, and already vaccine might be collected. 



This may be termed the period of crisis ; the appearances are most 

 characteristic. During the following days the vesicle is ruptured ; the 

 discharge continues from the ninth to the twelfth day, when the pustule 

 diminishes in size and dries up. After the fifteenth day crusts of a 

 brownish colour form ; these separate between the twentieth and 

 twenty-fifth days, leaving hard whitish-looking cicatrices, which per- 

 manently remain. 



Moderate itching accompanies the development of the eruption, the 

 principal functions are not disturbed, and fever only appears in the 

 event of the eruption becoming confluent or extending over a large 

 area. When the eruption is generalised the pustules or vesico-pus- 

 tules are found mostly in the region of the elbow, the lower border 

 of the neck, the flank and the inner surface of the limbs. They 

 present exactly the same appearance as the pustules on the surface 

 of the udder, but, being covered with hair, are less open to inspection. 



In certain rare cases the eruption extends to the perineum and 

 lips of the vulva. Signs of inflammation then develop on one or both 

 sides, the tissues display oedematous infiltration and disseminated or 

 confluent pustules. The lymphatic glands and vessels in the neigh- 

 bourhood of the pustules are always swollen. 



Causation. Cow-pox, or vaccinia, is a virulent disease transmissible 

 by accidental or intentional inoculation. The discharge from the vesico- 

 pustules and the crusts which afterwards cover them are virulent, 

 and inoculation can be performed by simply scratching the skin. A 

 first attack confers prolonged and sometimes perfect immunity, the 

 operation being successful if only one pustule develops. 



The disease is transmitted to healthy animals by milkers, by calves 

 in sucking, or by the conveyance in whatsoever form of virulent material 

 to sores or cuts. 



The nature of the parasitic or microbic agent which produces the 



