142 Lectures on Bacteria. [^ xii. 



bottom of Pasteur's culture-fluid when vegetation has ceased 

 and the nutrient-material is exhausted, and will remain there 

 alive and capable of renewed vegetation in a suitable substratum 

 for about eight months if the air has access to it, for a longer time 

 if air is excluded, as in hermetically sealed flasks. 



If the Micrococcus is taken fresh from a sick or dead bird 

 or from its excrements, or from an artificial culture abso- 

 lutely free from any diseased part of the bird, and introduced 

 into a healthy bird, the minutest possible quantity of it, ex- 

 hibiting ordinary growth and multiplication, will reproduce the 

 disease. Infection is obtained by inoculation in or beneath 

 the skin, and by introduction of the Micrococcus with the 

 food into the digestive canal. Pasteur succeeded in com- 

 municating the disease by inoculation to mammals as well as 

 to birds ; rabbits thus inoculated died ; in the case of guinea- 

 pigs abscesses only formed at the place of inoculation, and 

 these contained a large quantity of the Micrococcus, but 

 they did not spread and ultimately healed. Kitt has extended 

 these experiments with similar results to mice and sheep and to 

 a horse. 



Enough has been said to show that in this Bacillus, as in that 

 of anthrax, we have a facultative parasite specifically capable of 

 causing disease ; but its history and manner of life, especially 

 as regards the saprophytic sections of its development are not as 

 well known to us as those of Bacillus Anthracis. ' 



Pasteur further discovered that the Micrococcus loses to some 

 extent its power of infection when it is kept some time exposed 

 to the air ; the number of successful inoculations and the se- 

 verity of the attack caused by them diminish with the age of the 

 matter used in inoculation. The cases mentioned before of 

 slighter attacks of the disease ending in recovery are chiefly 

 cases of inoculation of this kind. We may say therefore in 

 words which have been used before that age produces an 

 attenuation of the power of infection or virulence of the 

 Micrococcus. 



