746 THE MICROSCOPE. 



their peculiar wriggling motion they were formerly- 

 called Vibrios ; Nageli named them " Schizomycetes." 

 Whether they are fungi, algae, belong to the genus Os- 

 cillatorise, or to the animal kingdom, is yet undecided. 



Bacteria are sure to be found wherever albuminoid 

 matter affords the material for sustaining life : in water, 

 in blood, in animal juices and secretions of all kinds : 

 in plants, in the sediment of waters, and upon glaciers 

 or the highest mountains. They appear in abundance 

 when organic matter is putrefying slowly and exposed 

 to the air. Their spores float in the air in every region, 

 and accumulate if the atmosphere is moist and bat little 

 jdisturbecl. Thus bacteria are easily obtainable for in- 

 vestigation, but it is only by the highest powers of the 

 microscope that it has been found possible to study 

 their development and variations. 



Most forms of bacteria once recognized that is, after 

 carefully conducted observations can scarcely again 

 be confounded with other bodies. Only the smallest 

 forms of micrococci or spheroidal bacteria present much 

 difficulty ; these may be mistaken for inorganic matter. 

 The chemical reaction of colonies of micrococci was 

 pointed out by Weigert. The granular mass is insoluble 

 in acetic acid, hydrochloric acid, caustic potash, gly- 

 cerine, alcohol, chloroform, and oil of cloves, and is not 

 killed by immersion in either of these agents. Hsema- 

 toxylin alum solution colours the mass dark blue, as 

 also does methyl violet solution if it is subsequently 

 washed in dilute acetic acid. 



So far, it appears that all bacteria consist of single 

 cells, and consequently their forms are not very mani- 

 fold. Four fundamental forms at least are recognized : 

 the spheroidal, rod-shaped, thread-like and spiral. 



The question naturally arises, are the different species 

 true, and confined to one definite form, or can one 

 species pass into that of another ? Hallier saw the 

 growth of bacteria into threads. Klebs saw the con- 

 version of micrococci into bacteria, and these into con- 

 tractile pigment granules. Billroth takes the funda- 

 mental form to be the spheroid bacteria Coccobacteria 

 septica ; these are said to multiply by elongation and 



