180 A MANUAL OF BACTERIOLOGY 



of the disease-germ, as in small-pox, relapsing 

 fever, malarial fever ; and in a still further set the 

 portal is just as often the respiratory tract as the 

 alimentary canal, or a wound of the skin, as in 

 anthrax, tuberculosis. But this does not mean that 

 the virus is necessarily limited to one particular 

 portal, or that it must be directly conveyed from 

 its source to the individual that it is to invade. 

 All this depends on the fact whether or not the 

 microbe has the power to retain its vitality and 

 virulence outside the animal or human body.' 1 



It must be borne in mind that not all the diseases 

 described in the present chapter can, at the present 

 time, be termed true microbian diseases ; yet with 

 the progress of science, and by following the lines 

 already laid down, we have not the slightest doubt 

 that in time the microbes of all the infectious 

 diseases will be discovered and cultivated. 



YELLOW FEVER. 



Micrococci (0*6 to 0'7 //, diam.) have been found 

 in the kidney, spleen, and liver during the course 

 of yellow fever. They form rosaries and masses, 

 which greatly distend the blood-vessels and give 

 rise to hemorrhages. The yellow-fever microbe is 

 termed Micrococcus amaril by Dr. Domingos Freire. 

 This microbe grows on gelatine, and reproduces the 

 disease in rabbits and guinea-pigs. If, however, 

 the microbe is cultivated in gelatine for six genera- 

 tions it loses the greater part of its virulence, and 



1 From a lecture delivered at the Royal Institution, London 

 (February 20, 1891), by Dr. E. Klein, F.E.S. 



