44 Manual of Veterinary Microbiology. 



and accumulations of dirt will yield to the atmos- 

 phere, under the influence of numerous agitations 

 of the air, particles contaminated with pathogenic 

 germs, which may have been brought there in various 

 ways. 



It was for a long time believed that the air expired 

 by the diseased was a fertile cause of the diffusion of 

 pathogenic germs in the atmosphere, but we now 

 know that the expired air never contains germs, 

 neither have we succeeded in transmitting diseases in 



this way. 



Transmission by the air has been accomplished ex- 

 perimentally for a certain number of diseases (sheep- 

 pox, charbon, tuberculosis, vaccinia, etc.) by the dis- 

 semination of the dried virus of these diseases in the 

 atmosphere. 



Under natural conditions the atmospheric germs 

 occur in a state of great dilution and hence the 

 chances of infection are extremely limited. If we add 

 that the air lends itself little or not at all to their 

 multiplication, and that they are destroyed more or 

 less rapidly by light, oxygen, and dessication, we shall 

 see that the danger from the free atmosphere is al- 

 most nil. 



The confined atmosphere of inhabited houses con- 

 tains more germs than the external air, that of cities 

 more than that of the country. 



The confined atmasphere of infected places can be- 

 come the carrier of disease germs and can transmit 

 certain contagious diseases either by transporting 

 these germs into the respiratory passages, or by de- 

 positing them upon alimentary matters or on the sur- 

 face of wounds. The pyogenic microbes have been 



