=Pathogenic Rod-Bacteria.= _Bacterium choleræ gallinarum_, an aerobic, facultative parasite which produces fowl-cholera among poultry; it is easily cultivated on various substrata as a saprophyte. The disease may be conveyed both through wounds and by food, and may also be communicated to mammals. _Bacillus anthracis_, the _Anthrax bacillus_ (Fig. 32), chiefly attacks mammals, especially herbivorous animals (house mice, guinea-pigs, rabbits, sheep, cattle), in a less degree omnivorous animals (including 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 (compare 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, but also deprive the blood of its oxygen. Vegetative cells only occur in living animals. This species is a _facultative parasite_ which in the first stage is a saprophyte, and only in this condition forms spores. [Illustration: FIG. 32.--_Anthrax bacillus_ (_Bacillus anthracis_) with red (_b_) and white (_a_) blood-corpuscles.] [Illustration: FIG. 33.--_Anthrax bacillus._ The formation of the spores; magnified 450 times.] _Bacillus tuberculosis_ produces tuberculosis in human beings, also in domestic animals (_perlsucht_). It is a distinct parasite, but may also live saprophytically. It is rod-formed, often slightly bent, and is recognised principally by its action with stains (when stained with an alkaline solution of methyl-blue or carbolic fuchsin, it retains the colour for a long time even in solutions of mineral acids, in contrast with the majority of well-known Bacteria): it probably forms spores which are able to resist heat, dryness, etc. _Bacillus lepræ_ produces leprosy; _Bacillus mallei_ produces glanders; _Bacillus tetani_, tetanus (the tetanus bacillus is very common in soil; anaerobic); _Bacillus diphtheriæ_, diphtheria; _Bacillus typhosus_, typhoid fever, etc. =Pathogenic Spiral Bacteria.= _Spirochæte obermeieri_ (Fig. 24) produces intermittent fever (febris recurrens); it makes its appearance in the blood during the attacks of fever, but it is not to be found during intervals when there is no fever. Obligate parasite.