316 ■ Sheep Pox. 



the vaccinating needle is used, which after the opening has been filled with lymph, 

 is stuck into the stretched skin in an oblique direction, in order that the vaccine 

 may enter the deep layers of the epithelium, and not under the skin; however the 

 skin may be also superficially scarified, and the vaccine rubbed into the scratched 

 area. 



In susceptible animals a typical pox exanthema develops if the vaccination 

 has been carried out properly, usually a single vesicle develops at each place of 

 pricking, others develop exceptionally in the surrounding parts, whereas a generalized 

 eruption of pox results only very exceptionally. 



The vaccinated animals should be kept isolated during the entire duration 

 of the local affection from sheep suffering from natural infection, as well as from 

 those which have not been vaccinated. After a period of about a week the vaccinated 

 animals should be examined individually, and in those which have failed to take 

 the vaccination the operation should be repeated. If the vaccination is negative 

 this time, although good lymph has been used, the respective animals should 

 be considered as immune. Vaccination with contaminated material may of course 

 result in various wound infections (necrosis of the skin, purulent inflammation of 

 the connective tissue, pyemia, tetanus). 



The vaccination of lambs is carried out in a similar manner, but usually with 

 lymph which was taken the previous year from vaccinated lambs, and kept in air 

 tight bottles in a cool room. 



Production and Preservation of Pox Lymph. In the first half of the last 

 century special institutions were established for the production of pox lymph in 

 France, and also in other countries, where the lymph originating from natural 

 benign pox was propagated in more or less constant virulence by continuous trans- 

 mission from sheep to sheep, and was increased in accordance with the demand. 

 Vaccination with such lymph usually resulted in very mild, localized pox, but it 

 was repeatedly noted that the artificially kept vaccine was capable, without any 

 apparent cause, of producing a generalized eruption, although in the meantime it 

 had Jfassed through 65, 98, and even 140 generations of sheep (Eoll). 



Eecently Soulie produced a vaccine in large quantities in the Pasteur Institute 

 of Algeria, by injecting single drops of lymph in various places into the clipped skin 

 of the rump of healthy sheep. In 10 to 12 days he collects the contents of the ripe 

 vesicles and stores them in a diluted state (see below). Every sheep treated in this 

 manner produces 500 cc. of diluted lymph, which is sufficient for the vaccination 

 of 10,000 animals. This vaccine has been used exclusively in Algeria for several 

 years, and the results are uniformly satisfactory; the lymph proves effective in 80% 

 of the cases, and the losses amount to' only 0.1-0.5%. The action of the lymph 

 however is not constant, as occasionally, especially in resistant breeds, the vaccina- 

 tion may be effective in only 20%, and even in only 8% of the cases (Martel). 



Borrel strengthens the virus by injecting pox lymph and then salt solution 

 mixed with bread crumbs into the pleural cavity of sheep. As early as in 4 to 5 days 

 a considerable quantity of a virulent fluid may be obtained from the thorax. 

 Another method of Borrel consists in injecting subcutaneously in the abdominal 

 region a mixture of 10 cc. of pox lymph and 500 co. of salt solution, of which 

 300-400 cc. is injected into the animal. The fluid, which should be rubbed over 

 as large a surface as possible, is usually absorbed by the third day, and from the 

 fourth day on a marked serous infiltration develops in the respective parts. On 

 the eighth day the animal is destroyed, and the fluid which has collected under 

 the skin, together with the infiltrated tissue, is ground in salt solution; in this 

 manner about two liters of a liquid are obtained, of which 1/20,000 of a cc. is 

 effective. 



Various methods are adopted for the preservation of the vaccine. The simplest 

 method consists in placing it in capillary tubes, or in fine glass tubes, the center 

 of which has been blown into spindle shape. The ends of such tubes, after filling, 

 are closed by melting, or sealed with sealing wax. 'For the same purpose two plates 

 of glass of 4 centimeters square may be used; the surfaces facing each other are 

 painted with the vaccine and the borders are closed either with mastix or wax. 

 The lymph may be also preserved in clean bottles, which are closed air tight. 

 (According to Peuch old lymph which on cutaneous vaccination is ineffective may 

 produce typical pox if injected subcutaneously.) SouliS stores the lymph with 

 2r5 parts of a 3% boracic acid, or 2% salicylate of sodium, and immediately 

 before vaccination he dilutes it v^ith 3 parts of its quantity, of boiled sterile water. 

 According to Bosc sheep pox virus remains unattenuated for at least two years 

 in the intestinal canal of leeches, which have sucked themselves full on opened, 

 ripe pox postules. 



Other Methods of Vaccination. In order to prevent a generalized eruption 

 of pox the attenuation of the virus was undertaken, but with unsatisfactory results. 



