BACTERIA. 39 



in materials containing sugar and starch, and the acid dissolves 

 the lime salts in the external layers of the teeth : those parts of 

 the teeth thus deprived of lime are attacked by other Bacteria, and 

 become dissolved. Inflammation in the tissues at the root of a 

 tooth, is probably produced by septic materials which have been 

 formed by Bacteria in the root-canal. 



DANGEROUS PARASITES. In a large number of the infections dis- 

 eases of human beings and animals, it has been possible to prove 

 that parasitic Bacteria have been the cause of the disease. Various 

 pathogenic Bacteria of this nature, belonging to the coccus, rod, 

 and spiral Bacteria groups, are mentioned in the following: 



Pathogenic Micrococci. Staphylococcus pyogenes aureus pro- 

 duces abscesses of various natures (boils, suppurative processes in 

 internal organs). The same effects are produced by 



Streptococcus pyogenes, which is the most frequent cause of malig- 

 nant puerperal fever ; it is perhaps identical with 



Streptococcus erysipelatis, which is the cause of erysipelas in 

 human beings. 



Diplococcus pneumonia (A. Friinkel) is the cause of pneumonia, 

 and of the epidemic cerebro-spinal meningitis. 



Gonococcus (Neisser) is the cause of gonorrhea and inflammation 

 of the eyes. 



Pathogenic Rod- Bacteria. Bacterium cholerce gallinarum, 

 an aerobic, facultative parasite which produces fowl-cholera among 

 poultry ; it is easily cultivated on various substrata as a sapro- 

 phyte. The disease may be conveyed both through wounds and 

 by food, and may also be communicated to mammals. 



Bacillus anthraci*, the Anthrax bacillus (Fig. 32), chiefly attacks 

 mammals, especially herbivorous animals (house mice, guinea-pigs, 

 rabbits, sheep, cattle), in a less degree omnivorous animals (includ- 

 ing human beings), and in a still less degree the Carnivores. 

 Aerobic. Cylindrical cells, 3-4 times as long as broad, united into 

 long rod-like bodies, which may elongate into long, bent, and 

 twisted filaments. Not self-motile. Endosporous. Germination 

 takes place without the throwing off of any spore-membrane (com- 

 pare Hay-bacillus p. 37 which resembles it). Contagion may take 

 place both by introduction into wounds, and from the mucous 

 membrane of the intestines or lungs, both by vegetative cells and 

 by spores ; in intestinal anthrax, however, only by spores. The 

 Bacillus multiplies as soon as it has entered the blood, and the 

 anthrax disease commences. The Bacilli not only give off poison, 



