BACTERIA OF THE MOUTH. 343 



2 or 3mm. in diameter before they begin to liquefy ; after th they extend 

 and liquefy very rapidly. 



2. A bacillus slightly constricted in the centre about 3;* in length, and 

 about one-half as thick as long ; in cultures it is similar to No. I, except 

 that it has a larger surface growth before it gives rise to any liquefaction. 



3. A bacillus very similar to No. 2, but with no constriction in the 

 centre ; it has square ends and frequently grows in long chains, especially in 

 liquid media ; it causes only slight softening of the gelatine. 



4. Is a small thin bacillus so short that it might even be mistaken for 

 a micrococcus ; it gives rise to a white growth along the needle track in 

 gelatine which it turns yellow, and then causes to liquefy. 



5. Was not found in all cases (in eight out of eighteen decayed teeth). 

 It is a bacillus with rounded ends, which grows almost exactly "ike No. I. 



6. Found five times only, is a large coccus ; it was found only in 

 advanced stages of decay, where the canals had been opened up by other 

 organisms as it was so large that it could not make its way along the 

 ordinary dentine canals ; it forms a white line along the track of the needle 

 in gelatine, of which it causes no liquefaction. 



The very favourable incubating chamber of the mouth is, 

 however, not monopolized by the organisms that so far have 

 been mentioned, and during epidemics, or when people come 

 in contact with persons suffering from various diseases, the 

 organisms associated with such diseases are, as might be 

 anticipated, frequently taken into the mouth, where they 

 accumulate, multiply, and eventually may set up any of the 

 various diseases with which they are associated in the hitherto 

 healthy person. 



In the very act of developing in the mouth they are sup- 

 posed to give rise to ptomaines and other poisonous products 

 which may render the human saliva toxic when introduced 

 by a bite or a wound into the individual himself, or into 

 another individual ; in fact, septic poisoning from injection 

 of the saliva from mad dogs was one of the great difficulties 

 with which Pasteur had to contend in his early experiments 

 on hydrophobia. Quite recently Sternberg, Fraenkel, 

 Klein, and others have shown that, though the pure saliva 

 as it runs into the mouth is non-pathogenic, it acquires toxic 

 properties as soon as it becomes mixed with the organisms 

 which are usually found in the mouth, this being especially 

 the case in patients suffering from certain infective diseases. 

 One observer has found that his own saliva is permanently 

 so toxic that it invariably causes the death of small animals into 

 which it is inoculated ; it is almost as fatal as hydrophobic 

 saliva. Some of these pathogenic organisms, like those we 

 have already mentioned, cannot be cultivated artificially, for it 



