Vaceination, Immunization. 351 



into the mouth of the next 6 to 8 cattle, and they are also allowed to chew 

 upon it. Less certain is the procedure in which threads impregnated with saliva 

 of affected animals are inserted into the subcutaneous connective tissue of the 

 ear, or of the tail; the feeding of affected milk is less commendable, as this may 

 sometimes produce a severe gastro-intestinal catarrh. 



Twenty-four to 48 hours after inoculation the temperature of the animals 

 commences to rise, and 2 to 3 days later vesicles appear on the mucous membrane 

 of the mouth, exceptionally also between the hoofs, which continue to develop in 

 the usual form until recovery takes place, mostly in the course of the second 

 week. The inoculated animals should be subjected to the same treatment that 

 they would have received had they contracted the disease by natural infection. 



Other animals than cattle are usually not' subjected to the inoculation as it 

 is usually less certain in them, e. g. in hogs (in these it may be undertaken on the 

 snout with the aid of an inoculation lancet). 



II. Immunization. Althougli animals may easily be im- 

 munized by the deliberate production of the disease, and the 

 immunity thus produced as a rule lasts for a long time, yet 

 such a procedure fails to meet the requirement that the immun- 

 ity be produced without a pronounced affection of the animals, 

 especially without the development of the vesicular exanthema. 

 Attempts to work out a method, which would be sufficiently effec- 

 tive, and at the same time without danger, have so far produced 

 only partially satisfactory results, in establishing the possi- 

 bility and the nature and method of passive immunization, 

 while the problem of general immunization is not solved at 

 the present time. 



1. Active immunization. For this purpose either pure 

 lymph or a mixture of lymph and immune serum have been 

 used, however, without practical results, and in some instances 

 even with unfavorable effect. 



Nosotti in Northern Italy attempted to immunize cattle, by injecting them 

 subcutaneously with pure lymph taken from closed vesicles, diluted with aqueous 

 humor or blood serum, the results however were not satisfactory, as a considerable 

 proportion of the inoculated animals became affected in the usual way. 



' According to Loffler and Frosch, virulent lymph which has been subjected for 

 12 hours to a temperature of 37°, may produce an immunity if injected into the 

 blood in quantities of 0.01-0.1 cc. As however this method is effective only in 

 30 to 50% of the cases the procedure has not been inaugurated in practice. 



Lofier and Frosch later found that a mixture of virulent lymph and blood 

 serum from artificially hyper-immunized animals (1/50-1/40 cc. lymph plus 10-20 cc. 

 blood serum), if^ allowed to stand for a short time, and then injected subcutaneously 

 into cattle and hogs, produces only a passing febrile affection, without the develop- 

 ment of a vesicular exanthema. The animals however become immune so that 

 in 3 or 4 weeks they stand an inoculation with 1/50 ce. of virulent virus without 

 danger. 



The mixture of lymph and blood serum was placed on the market at the end 

 of 1898 under the name of " Seraphthin, " but it did not prove satisfactory in 

 practice. In different localities a large portion of the inoculated animals became 

 affected with typical foot-and-mouth disease (Flatten, Schrader, Schmidt, Leonhardt, 

 Lothes and others) while the disease produced by the inoculation was sometimes 

 malignant, and even fatal (Schindelka, Geist). Equally unfavorable results were 

 obtained from application of Hecker's vaccine. 



In Loffler 's later procedure (1905) the cattle to be immunized received sub- 

 cutaneous injections, first of 0.5 cc. of highly valent cattle serum, and 0.03 cc. of 

 fresh virulent lymph. After 24 to 26 days they receive, also subcutaneously, 0.0033 

 ce. of lymph, 12 to 14 days later 0.01 cc, and after another 12 to 14 days 0.04 cc. 

 This method has not been tried in practice because of its impracticability. 



The most recent experiments of Loffler show that in the inoculation of a 

 lymph serum mixture, the quantity of serum must be in a certain proportion 

 to the lymph if it is desired to produce a uniform immunity, and that the lymph 



