DISEASES OF SHEEP. 55 



proper vaccine-matter and for the use of the same at a 

 proper time, otherwise an unfavorable or dangerous result 

 may be the consequence. According to experience, segre- 

 gated lymph forms the best vaccine-matter ; such lymph is 

 to be collected from natural pox, on the sixth or seventh 

 day after eruption. It must be perfectly clear and fluid, 

 like water. Thick, turbid and suppurated lymph produces 

 in most cases no pox, or only a sore, and the use of the 

 same offers no protection at all. It may, however, happen 

 that a sufiicient quantity of clear lymph cannot be obtained 

 from natural pox (especially when there are great numbers 

 to be vaccinated). In such a case the blood emerging 

 from the incision of natural pox may be used as a perfectly 

 satisfactory substitute for lymph. Among the sheep which 

 I have had occasion to vaccinate, at least thirty thousand 

 have been vaccinated with such kind of blood (for want 

 of lymph), and the result proved to be entirely of the same 

 satisfactory character. The same observation occurred to 

 many other professional men and owners of sheep. It ap- 

 pears, therefore, that no difference exists between vaccina- ' 

 tion with clear lymph and that with the blood or bloody fluid 

 of the pox ; if, however, plenty of lymph can be had, the 

 latter is preferable. In case such clear lymph cannot be 

 procured, the blood must be taken from pox which has ar- 

 rived at the so-called state of maturity, especially when 

 such pox still contains a small portion of clear lymph ; the 

 upper skin of such pox must be of a bluish-white color and 

 already separated from the textures below. Care must be 

 taken to select only such pox the maturity of which is not 

 already perfected ; the blood of perfectly ripened pox 

 {being covered with a very thick and perfectly white skin 

 and tending to fall off) is in many cases of no avail. It is 

 further advisable to take the vaccine-matter from young, 

 strong and otherwise healthy animals, where the pox is of 



