160 THE INVISIBLE WOKLD 



sandth part of an inch. Considerably less in its 

 shorter diameter. It propagates by the production 

 of spores. Sometimes the germs are seen in pairs, 

 each pair surrounded by a capsule. 



A second form of the disease is named catarrhal 

 pneumonia. It is to the lung something like ca- 

 tarrh to the nasal organs. The bronchial tubes and 

 the air cells of the lung are inflamed. Excretions 

 are abundant. The air passages are congested 

 sometimes closed. This last means death. 



The germ that causes this second form is similar 

 to that of the first similar in size, and shape, and 

 propagates in the same way. But it differs from 

 the first in forming itself into chains as represented 

 in Fig. 77. 



Two other forms are called septic pneumonias. 

 They are caused by microbes which produce at 

 once septic, or putrid, conditions in the lung. 

 Sometimes they enter the lung by way of the air 

 passages. At other times they come to the lung 

 directly from some boil ; carbuncle, or other sup- 

 purating wound, on the surface of the body. In 

 the pus of such a wound are millions of the germs. 

 By the circulation of the blood from the wound to 

 the lung the germs are liable to be carried to that 

 organ. When this is the case, they set up the 

 same conditions in the lung which they set up in 

 the wound whence they come. It is simply trans- 

 ferring, by the bloodstream, the disease at the sur- 

 face to the lung. First, inflammation in the lung, 



