De Zouche. — Bacteria and their Relation to Disease. 41 



Two cocci attached to each other are spoken of as a diplo- 

 coccus, while several cocci attached to each other in the 

 form of- a chain are called streptococcus, from o-TpeVros, a 

 chain. Then there is the vibrio, or bentrod ; the spirillum, a 

 corkscrew form ; bacillus, a long thin rod, &c. 



Bacteria multiply by fission and by spores, or by cells 

 wdiich act as spores. From their mode of reproduction by 

 fission they are called schizomycctcs or fission-fungi. 



Bacteria require for their nutrition nitrogen, carbon, 

 potassium, sodium, and phosphoric acid, while water is neces- 

 sary as a medium for the changes operated by them. Their 

 food is obtained from organic compounds, which they have 

 the faculty of splitting up, but they also grow in solutions of 

 tartrate and acetate of ammonia. Some require the presence 

 of free oxygen ; hence Pasteur makes two great divisions of 

 bacteria into (1) aerobic, and (2) anaerobic. Their growth is 

 affected by the soil in which they happen to be planted ; also 

 by temperature, by contact with oxygen, &c. ; in other words, 

 by their environment. Thus the bacillus of anthrax and the 

 micrococcus of fowl-cholera, so malignant under ordinary 

 circumstances, have been rendered harinless by cultivation in 

 neutralised chicken-broth with a supply of oxj'gen and in a 

 heightened temperature ; or, as some assert, through the 

 action of the heightened temperature alone. Just as human 

 beings and animals may become stunted and deformed by 

 starvation and want of light and warmth, so may bacteria 

 become altered in form, and exhibit a sickly growth; or, on the 

 other hand, w4th suitable food and other accessories they may 

 grow luxuriantly. We find similar phenomena in the higher 

 plants. " Bishop Heber mentions that in the Botanical Gardens 

 at Calcutta he saw a wretched little oak kept alive with 

 difficulty, under a sky and in a temperature so perpetually 

 stimulating that no time was allowed it to shed its leaves, or 

 to recruit its powers by hibernation."''' Bacteria which grow 

 in living bodies are termed parasites ; those growing in dead 

 bodies or decaying organic matter are called saprophytes. 

 That fungi can be parasitic in living bodies we have a striking 

 example in the Cordiceps, which grows at the expense of the 

 caterpillar which it infests, filling the body with its myce- 

 lium, and causing the death of the animal. Some bacteria — 

 as anthrax, for example — can live and vegetate either as para- 

 sites or as saprophytes ; and, further, they can live in decaying 

 vegetable matter, such as potatoes, and this is a special 

 source of danger to animals, which are thus liable to become 

 infected by their vegetable food. They have distinct pre- 

 ferences as to their host, resembling in this respect many 



* " Geograpli. Distrib. of Plants." Relig. Tract Society. 



