14 D. H. ATTFIELD — THE lOWEK MICHO-OEGATflSMS. 



that the air constantly contained various putrefactive and fermen- 

 tative germs, and also that fermentative processes were dependent 

 on the access of living organisms. Since that time, owing to the 

 labours of such renowned workers as Pasteur, Koch, Klebs, and 

 Du Bary abroad, and Klein, Crookshank, Sims-Woodhead, Watson 

 Cheyne, and many others in our own country, steady progress has 

 been made in the knowledge of these organisms, which may be 

 well termed, as I have said, our invisible friends and foes. 



As to a classification of the micro-organisms for general purposes, 

 the best will be that depending on their physical form. Microbes 

 consist of single cells composed of that wonderful complex organic 

 substance called protoplasm, surrounded with an envelope of a 

 cellulose-like substance, and may be thus classed : — 



(I.) Cells more or less spherical, termed cocci. 



(II.) Cells more or less cylindrical, known as bacilli. 



The first class, with spherical cells, is divided into several groups. 

 (a.) Single separate round cells known as micrococci. {b.) Two 

 such cells in more or less close contact ; these are termed diplococci. 

 (c.) Several cells joined one to the other to form a chain ; these are 

 therefore called streptococci, (d.) A large number of cells in 

 close contact with each other, forming an irregular bunch, of 

 grape-like structure, known as staphylococci, {e.) Spherical cells 

 grouped in a peculiar way, resembling a bale or bundle of goods 

 corded round in three directions, and known as sarcinte. 



The second main division, with cylindrical cells, has a number 

 of subdivisions depending on the various length, thickness, or 

 curvature of the members, and contains such genera as Bacillus, 

 Lcptotlirix, Sjiirillum, and some others which need not be mentioned 

 here. 



Having thus roughly classed the microbes, I will say a few 

 words as to how they are grown for experimental purj^oses and 

 also shortly touch on the methods of bacteriological research. 

 This is all the more necessary owing to the fact that Bacteriology, 

 the name of the science which deals with these micro-organisms, is 

 of quite recent growth, and is but little understood except by those 

 who make the subject a special study. Everyone can imagine how 

 the scientific chemist works with his test-tubes, and stills, and so 

 on ; most people understand or can picture how the anatomist 

 works by aid of his knife and microscope ; but the case is quite 

 different when we come to study the methods of the bacteriologist, 

 whose science, as I have said, being of much more recent date, the 

 various tenns used by him convey but little information to the 

 uninitiated. These micro-organisms are not only ubiquitous, but 

 are present also in enormous quantities. In our food, and on our 

 bodies and clothes, they are met with in vast numbers. The mouth 

 is a very good forcing- ground for several species. If one is un- 

 fortunate enough to have a decayed tooth the bacteria thrive all 

 the better. A tiny drop of moisture from such a carious cavity is 

 spread over a thin microscopic cover-glass, dried, and then treated 

 with a colouring solution of gentian-violet. The excess of staining 



