Tea VERS. — 0)i Pathogenic Microbes. 59 



quantity. In order to obtain numerous specimens it is enough 

 to take half a glass of ordinary water from a spring or river, 

 and to leave it for some days on a table or chimney-piece, the 

 vessel being uncovered to allow the access of air. We may 

 soon observe that a thin coating is formed on the surface of 

 the water which looks like a deposit of fine dust, but which, 

 however, consists of myriads of bacteria. If we take a drop 

 of this water and place it under a cover-glass in order to 

 examine it under a microscope with a magnifying-power of 

 about 500 diameters, we shall, as soon as the instrument is 

 properly focussed, see a really surprising spectacle. 



' ' The whole field of the microscope is in motion : hun- 

 dreds of bacteria, resembling minute transparent worms, are 

 swimming in every direction with an undulatory motion like 

 that of an eel or snake. Some are detached, others united in 

 pairs, others in chains or chaplets, or cylindrical rods, which 

 are partitioned or articulated : these are only less mature, or 

 3'ounger, than the first. Finallv, we see a multitude of small 

 globules which result from the rupture of the chaplets. All 

 these forms represent the different transformations of Bacte- 

 rium termo, or the microbe of putrefaction. Those which are 

 dead appear as small, rigid, and innnovable rods." 



In all the various forms of microbe, however, each cell 

 consists of a cellulose wall containing protoplasm. These 

 cells, so long as they continue active, multiply by fission with 

 enormous rapidity, precisely in the same way as in the case of 

 ferments. When, however, the liquid upon which they sub- 

 sist is dried up, the cell-wall dries also, and the protoplasm 

 within contracts and forms a spore, which, being set free by 

 the rupture of the wall, gives rise to fresh microbes by ger- 

 mination when placed under suitable conditions. 



Pathogenic microbes, then, are extremely minute cells, 

 invisible except under very high powers of the microscope, 

 having walls composed of cellulose, enclosing particles of 

 protoplasm, multiplying rapidly whilst active by fission, and, 

 when no longer capable of increasing in this manner, pro- 

 ducing spores which, on finding a suitable soil, produce afresh 

 crop by germination. 



Microbes .themselves and their spores, as well as the 

 spores of moulds and ferments, are extremely light, and float 

 in the atmosphere amongst the innumerable other particles of 

 matter which reveal their presence to the naked eye by re- 

 flecting light, as may be observed when a ray passes through 

 a narrow opening into a darkish room. Elaborate investiga- 

 tions have been made in Europe — chiefly in France — with a 

 view to obtain statistical information as to the hygienic condi- 

 tion of the air of towns, according as it is more or less charged 

 with these minute organisms. 



