334 



Swine-Fever. 



[august, 



to the pig when inoculated, but it would still cause swine- 

 fever by inoculation, because the virus of that disease 

 is not retained in the pores of the filter. The swine-fever 

 microbe, unlike the anthrax bacillus, is too small to be seen 

 by the highest powers of the microscope, and for this reason 

 it may also be described as an ultra-microscopic virus. That 

 there is a specific and infective agent, however, is not open 

 to doubt, notwithstanding the fact that it cannot be seen, 

 for swine-fever can certainly be produced in susceptible pigs 

 by inoculating them with the filtered or unfiltered blood of 

 diseased pigs. 



Incubation Period. — The incubation period, that is to say, the 

 time which elapses between contact with infective material 

 and the appearance of the first symptoms, is about five days. 

 It is not to be concluded, however, that very distinct symptoms 

 will always be noticed at such an early date. The first sign 

 of infection is usually little more than a rise of temperature, 

 which can only be ascertained by using a thermometer. In 

 most outbreaks, the distinct signs of illness do not appear for 

 eight or ten days, or even more, and this has led to mistaken 

 views being held on the length of the incubative period. In 

 some outbreaks, however, the virus is so potent that the 

 distinct symptoms may appear much earlier, and the swine 

 attacked may be dead in less than ten days. 



Symptoms. — For the information of the pig owner, it will be 

 useful to describe the symptoms as much in relation to an 

 outbreak as to the individual pig. Young swine are, as a 

 general rule, more severely attacked than others. It seems 

 probable that the virus of swine-fever possesses varying grades 

 of virulence, and that in consequence, the severity of out- 

 breaks differs. As seen in this country, the outbreaks of swine- 

 fever might be referred to three principal classes, which tend 

 to approach each other as the surrounding circumstances 

 alter. 



I. There may be a very virulent outbreak which is 

 characterised at the start by a very short period of illness and 

 a large number of deaths at one time or at short intervals. 

 In such cases the temperature of the sick animal rises to 

 io6°-7° F. The affected animals refuse food, and bury 

 themselves in the dry litter, or, if no litter is available, they 



