10 



exposed to it naturally, ñor is it possible to give them the 

 disease by inoculating them with virulent material. Vaccinat- 

 ing calves against blackleg increases their immunity or power 

 to resist the disease for about six months, after which time 

 the immunity grows less. Calves should be vaccinated against 

 blackleg every six months from the age of two months until 

 they are 18 months oíd. They should be vaccinated about 

 the first of September to protect them for the next four months 

 when the losses from this disease are greatest, and again 

 about the first of April. Calves inay be vaccinated at any 

 season of the year and this should always be done if cases of 

 blackleg occur on the farm or iu the locality. 



BLACKLEG VACCINE. 



Blackleg vaccine is prepared as followü. A calf is 

 inoculated with virulent material and when the disease is 

 fully developed the calf is sacrificed and the afifected muscles, 

 those having a dark bruised appearance, are collected, cut 

 into thin strips, dried, ground and weakened or attenuated 

 by heating for six hours in a specíally prepared oven at a 

 temperature of about 91 o C. This powder, after it is very 

 hnely ground and sifted, is put upin small envelopes contain- 

 ing 10 or 25 doses. After the vaccine is prepared it should be 

 carefully tested before it is sent out. 



Blackleg vaccine should be fresh. It should not be used 

 if it is more than three months oíd as this vaccine loses its 

 strength if kept long iu a tropical climate. The envelopes 

 containing the vaccine shoud be kept iu a cool dry place and 

 not opened until they are to be used as there is danger of 

 other germsgettingin the vaccine. Some coinmercial vaccines 

 are put upin other than powdered forms. In using commercial 

 vaccines be sure that they are fresh. 



VACCINATING INSTRUMENTS. 



The instruments necessary to use the powdered blackleg 

 vaccine are a small glass or porcelain mortar and pestle, a 

 small glass gradúate of 25 c. c. capacity a wide mouth glass 



