238 



BACTBPJOLOGY 



on the other hand, the teeth become so altered by the acidity 

 as to furnish a suitable nidus for their growth (Miller) . 



If solution of iodine and potassium iodide be added to 

 a sample of fresh saliva, many fibres are seen which are 

 coloured yellow and intertwined with one another. These are 

 described as Leptothrix buccalis. Others stain bluish-violet 

 with tincture of iodine, appear in tufts, and are called the 

 Bacillus buccalis maximus (fig. 89). Micrococci which 

 appear bluish- violet after the addition of tincture of iodine 

 bear the name of lodococcus, amongst which Miller distin- 

 guishes by cultivation an lodococcus magnus and an lodo- 

 coccus parvus. Some- 

 times cocci are stained 

 blue and their sheath 

 yellowish by tincture 

 of iodine (lodococcus 

 vaginatus), and some 

 stain rose-red. Infec- 

 tions of the teeth 

 leading to caries are 

 supposed by Miller to 

 be due to the fact that 

 in acid solutions the enamel loses the lime it contains 

 and grows soft, this softened substance then forming the 

 gelatinous ground-substance which is altered just like 

 gelatine by the action of micro-organisms, so that damage 

 to the tooth results, leading to caries. 



Micrococcus salivarius septicus and Bacillus salivarius 

 septicus. — Biondi found both micro-organisms in saliva, the 

 bacillus in healthy as well as diseased individuals, the 

 micrococcus in puerperal septiccemia. 



The Micrococcus salivarius septicus consists of round or 

 sometimes oval cocci, the growth of which does not liquefy 

 gelatine. Upon plates round colonies form which are dark- 



Fic. 89. — Leptothrix buccalis. (After Jakscli.) 



