352 I'oot-and-Mouth Disease. 



should be attenuated by the serum only to the extent that it should prevent 

 its disease producing action, but should not entirely render it ineffective, that is, 

 it should still be able to produce a reaction in the body for the establishment of 

 an immunity. The difficulty of measuring the quantity of the lymph and serum 

 accurately can of course hardly be overcome, and therefore, at least at present, 

 there is very little possibility that immunization based on this principle will prove 

 practical. 



Ory recommended cow pox lymph as a vaccine against foot-and-mouth disease, 

 inasmuch as he supposed that in the close relation of the two diseases there exists 

 a reciprocal immunizing" relation. He first inoculated horses with calf lymph, and 

 used the lymph from the vesicles for the vaccination of cattle. These are claimed to 

 have proven immune against foot-and-mouth disease after passing through a mild 

 inoculation disease. Confirmation tests by Anker and Starcovici, Calinescu and 

 Sitaru however proved that it is not possible to produce immunity in this mannerj 

 and Seibert could not obtain practical results from the use of original pox 

 lymph. 



The Eoumanian authors just mentioned later modified the procedure, in 

 using as a vaccine a mixture consisting of two parts of cow pox lymph, two parts 

 salt solution, and one part foot-and-mouth disease lymph. The practical value of 

 this method is supposed to be found in that the animals only become mildly affected 

 and in the meanwhile may be used for work (the danger of spreading the disease is 

 of course present in the same degree in this procedure as in the emergency inocu- 

 lations). 



2. Passive immunization. Blood serum from animals which 

 have passed through foot-and-mouth disease, in quantities from 

 500 to 1,000 cc, increases the resistance of the susceptible ani- 

 mals; by the repeated intravenous injections of virulent lymph 

 this resistance may be increased to such an extent that the 

 serum, even in small doses, will produce a passive immunity. 

 In this way cattle may be immunized for a period of several 

 weeks, and by serum inoculations repeated at intervals, the 

 immunity may be prolonged even for several months. 



A single serum inoculation would then be indicated only 

 in those cases in which it is desired to protect the animals for 

 a period of about three weeks; thus, for instance before they 

 are taken to stock shows or to markets. On the other hand 

 inoculations repeated two or three times, at intervals of 10 

 days, may serve beneficially in the eradication of the disease, 

 inasmuch as by such a treatment of animals threatened with 

 infection, its spread to surrounding herds may be prevented, and 

 thereby the results from other measures of eradication and 

 prevention may be assured. 



LofSer's method of preparing the immune serum is as follows: For the im- 

 munization of large animals a virus propagated in the body of pigs weighing 15 to 

 20 kg. is used. The pigs are inoculated with 1/25 cc. of lymph, whereupon they 

 become ill in from 2 to 3 days, and the lymph is collected from the vesicles. They 

 then receive subcutaneously 10 cc. of immune horse serum, which results . in their 

 recovery. The lymph, which is filtered through a porcelain filter, is inoculated 

 intravenously to cattle in increasing quantities, and after such treatment for 2 1/2- to 

 3 months they produce a sufficiently potent serum. The serum is suitable for practi- 

 cal application when 100 cc. protects oattle of 200-252 kg. weight against an in- 

 travenous injection of 0.1 cc. of virulent lymph, 24 hours later. Twenty ec. of 

 serum neutralizes the action of 0.05 cc. of lymph; as in the natural infection 

 usually only small quantities of virus produce the disease, it is sufficient, except 

 in unusually severe cases, to use 20 cc. of serum for immunization purposes. In 

 already affected animals the outbreak of the disease is prevented only by a con- 

 siderably greater quantity (100-200 ec), and even then not with certainty. • 



