848 THE FILTRABLE VIRUSES 



of eleven guinea-pigs and have shown that the blood of these animals is infective 

 for monkeys. 



Cows, sheep, goats, pigs, asses, dogs, rabbits, rats and fowl appear to be 

 naturally immune to the virus of typhus fever. 



Etiology. Nicolle, Comte and Conseil were able to transmit the virus of 

 typhus fever from an infected Macacus sinicus to two other bonnet monkeys 

 by means of body lice (Pediculus vestimenti). This observation has been con- 

 firmed by Bicketts and Wilder in America. According to Goldberger and 

 Anderson the virus can also be transmitted by Pediculus capitis. 



To ensure infection by means of lice a considerable number of insects 

 should be employed. Ricketts and Wilder have adduced evidence which goes 

 to show that the virus of typhus fever multiplies in the bodies of lice and that 

 the infection may possibly be transmitted to a second generation of the insects 

 a fact of considerable interest and importance. It would appear that lice 

 are capable of infecting a new host a week after being fed upon an infected 

 individual. 



