VACCINATION OF CATTLE 331 



With other observers this method of vaccination has always given favour- 

 able results, but complete immunity has not been attained. 



Vallee and Rossignol undertook a series of control experiments on twenty calves 

 each about 5 months old which had not reacted to tuberculin. These animals were 

 first inoculated in the jugular vein with 4 mg. of dried tubercle bacilli (bovo-vaccin 

 of von Behring) and 3 months later with 20 mg. of similar bacilli. They were tested 

 by ultra- venous and sub-cutaneous inoculation and by being kept in contact with 

 animals suffering from open tuberculous lesions. From these experiments, Vallee 

 and Rossignol conclude that von Behring' s method of vaccination is harmless to 

 animals protected from sources of accidental infection during the period of immuniza- 

 tion and for 6 weeks afterwards : that the vaccination confers considerable but not 

 absolute powers of resistance to the most severe methods of infection and that the 

 vaccinated animals are able to resist for some months spontaneous infection which 

 might have been expected to arise from prolonged contact with infected animals. 



Von Behring's method of vaccination should be performed on animals 

 less than 3 months old. In calves more than a year old the vaccinating process 

 occasionally sets up a violent reaction and is dangerous to life. The severity 

 of this reaction seems to depend upon an anterior infection with tuberculosis 

 and it is well known that in cattle the younger the animal the more rare the 

 disease. The resulting immunity is especially noticeable when the animals 

 are tested by intra-venous inoculation but is only effective for a few months 

 when tested by feeding the animals with infected food stuffs or keeping them 

 in contact with cattle suffering from open tuberculous lesions. 



(ii) With a view to getting more constant results and a more efficient 

 method of vaccination some observers have experimented with living and 

 virulent bacilli of the human type. Experience has shown that the immunity 

 produced in cattle by the inoculation of living cultures runs parallel with the 

 virulence of the tubercle bacillus used in the experiments, the higher the 

 virulence of the bacillus the greater the degree of immunity produced. 



[A. S. Griffith and F. Griffith (English Commission) investigated the produc- 

 tion of immunity in calves by the inoculation of living tubercle bacilli. Twelve 

 calves were inoculated sub-cutaneously or intra-venously, ten with human 

 and two with bovine tubercle bacilli and were subsequently tested as to their 

 resistance by the sub -cutaneous inoculation of a large dose (50 mg.) of bovine 

 tubercle bacilli. Nine of the calves " had their resistance so far increased 

 that 50 mg. of bovine tubercle bacilli were unable to set up in them pro- 

 gressive tuberculosis." Of the remaining three two died of acute tuberculosis 

 and the third when killed showed general tuberculosis but in a less severe 

 degree than in any of the four control animals. Thus " by the inoculation 

 of large doses of human or small doses of bovine tubercle bacilli, the resistance 

 of a calf can be raised sufficiently to protect it against the inoculation of a 

 dose of bovine tubercle bacilli capable of setting up a severe and fatal tuber- 

 culosis in a calf not so protected " ; but " this degree of resistance is not 

 always produced." There was no evidence to show that vaccination with 

 bovine tubercle bacilli produced a higher degree of immunity than vaccination 

 with human tubercle bacilli. ] 



Bacilli killed by heat are devoid of vaccinating properties. 



But vaccination with an active virus is not free from danger ; inoculation 

 of living bacilli of the human type may [it is said] set up latent lesions 

 which can be re-awakened and constitute a permanent menace of re-infection ; 

 and finally, it is a danger to the consumer of the meat [and milk]. 



[A. S. Griffith (English Commission) found that if milking cows are " inocu- 

 lated sub-cutaneously or intra-venously with tubercle bacilli of relatively 

 slight virulence such bacilli quickly appear in their milk and may continue 



