72 The Story of the Bacteria 



entirely unknown; indeed, it . was only an 

 hypothesis that the disease was due to germs 

 at all. 



A great deal of careful laboratory work has, 

 however, been done on this subject, and a 

 great many animal experiments made, so that 

 now we know not only that 

 blood poisoning but boils, 

 abscesses, erysipelas, and 

 many other less serious in- 

 flammations are induced by 

 bacteria. We have found 



FIG. 8. STREPTO- c .* ,-, ... 



coccus PYOGENES out furthermore, that there 

 are two particular species 

 which cause the trouble in the great majority 

 of cases. 



Both of these bacteria are little balls or 

 micrococci. One of them, as it grows, tends 

 to form chains, and so is called Streptococcus 

 (Fig. 8) ; the other tends to group itself in 

 clusters a little like a bunch of grapes, and 

 so is called Staphylococcus (Fig. 9). 



Now, it has been further found that these 

 two forms of bacteria are quite abundant 

 where people are gathered, mostly in dirty 



