346 TEXT-BOOK OF BACTERIOLOGY. 



They regularly appear in characteristic groups of four, inclosed in 

 a common capsule. 



The latter is beautifully developed after injecting the bacteria 

 into the abdominal cavity of Guinea-pigs. A very considerable 

 purulent peritonitis is found on dissection ; microscopic examination 

 shows that the accumulated masses of viscid mucus coating the in- 

 testines with a dense, compact layer, consist almost entirely of cocci 

 with their greatly swollen capsules. 



Having thus far treated of the bacteria in general, ascertained 

 the properties of these micro-organisms, and become aquainted with 

 a number of the better-known non-pathogenic and pathogenic bac- 

 teria, we shall now proceed to discuss the final part of our task, 

 viz.: the application of recent methods of investigation to the chief 

 constitutents of our natural surroundings, the air, soil, and water. 



