VACCINATION 557 



To attenuate the product some of the powder is mixed with twice its weight of 

 sterile water, spread in a thin layer and heated at 100 C. or 105 C. for 5-6 

 hours. This constitutes the first vaccine and on inoculation leads to no untoward 

 symptoms. 



Another portion of the powder is similarly moistened and heated for 5 or 6 

 hours at 90 or 94 C. only. This is the second vaccine ; it is more virulent than 

 the first and is dangerous to inoculate in the first instance. 



To vaccinate an animal emulsify in a mortar the contents of a packet of 

 the first vaccine with 10 c.c. of boiled water, stirring meanwhile. Filter the 

 emulsion through a piece of fine linen and inoculate 1 c.c. of the filtrate into 

 the tip of the tail (or into the tip of the ear) after cutting the hair and washing 

 the skin with soap and water. Some days later the immunity is strengthened 

 by inoculating the second vaccine. 



The immunity is permanent and accidents are uncommon. If the reaction 

 be over-violent, which is not the case if the inoculation has been properly 

 done, the animal's tail should be cut to remove the focus of infection. The 

 method is now extensively practised in France and Switzerland. 



The full virulence of the powder can be restored if necessary by mixing a little 

 lactic acid with it ; the acid produces a small necrotic focus and prevents the leuco- 

 cytes reaching the site of inoculation, and so allows the organism to develop. 

 Alcohol, trauma and certain micro- organic toxins act in the same way. The organism 

 in the powders is never really attenuated : it is true that the virus is modified but 

 only in the sense that its germination is retarded, during which time the inoculated 

 tissues have time to arrange their phagocytic defences. Proof of this view is 

 furnished by the fact that when a little of the powder is sown on artificial media a 

 virulent culture is obtained. 



Arloing's powders contain numerous impurities since contaminating micro- 

 organisms are present in very large numbers in the swelling. It is to these 

 latter that the occasional accidents which occur during vaccination are to 

 be attributed. Leclainche and Vallee have described a method by which 

 vaccines containing pure cultures of the organism may be prepared : 



The heart blood of a guinea-pig or sheep dead of quarter ill is collected and incu- 

 bated in sealed capsules for 48 hours at 37 C. The contents are then spread in 

 thin layers in sterile Petri dishes and kept in the incubator at 37 C. until desiccation 

 is complete. The dried blood is powdered and rubbed up with a little sterile water. 

 This paste is spread in thin layers on glass plates and divided into two portions. 

 One is heated in an hot air chamber for 7 hours at a temperature of 102 C. (first 

 vaccine), the other at a temperature of 92 C. (second vaccine). The vaccines are 

 powdered and stored in sterile tubes in the same way as Arloing's. 



Note. Pure vaccines behave like spores of the bacillus in that they are not mixed 

 with toxin and are not fatal to animals in moderate doses, but on the other hand 

 they are efficient for purposes of vaccination which is not the case with pure spores 

 (obtained by heating cultures to 80 C. for 3 hours). If spores be inoculated they are 

 phagocyted immediately, whereas the physical state of the vaccine when inoculated 

 to a certain extent retards phagocytosis so that the destruction of the spores is 

 delayed until the tissues have had time to elaborate antibodies, which antibodies 

 constitute the immunity of the animal. 



(iii) Kitasato and also Kitt state that the inoculation of broth cultures 

 more than a fortnight old does not kill guinea-pigs but confers immunity 

 upon them, and that virulent cultures heated at 80 C. for 30 minutes have 

 similar vaccinating properties whereas if heated at 80 C. for 3 hours these 

 properties are destroyed. 



(iv) Leclainche and Vallee have shown that virulent cultures heated at 

 70 C. for 2 hours do not kill young guinea-pigs but are toxic for adult guinea- 

 pigs. One c.c. of a culture treated in this way confers a lasting immunity 

 on young guinea-pigs : 2 c.c. inoculated into cattle behind the shoulder 



