442 REPORT— 1893. 



of bacteriological problems can be, and have been, solved by experimenting 

 with casual mixtures of microbes, progress in many directions was neces- 

 sarily barred until particular organisms could be obtained and maintained 

 in a state of purity for investigation. 



That these methods have now reached a high state of perfection is 

 attested by the fact that, in spite of the great number of persons who are 

 constantly using them in all parts of the world, no changes of any great 

 importance have been made during the jaast few years. A general under- 

 standing of these methods of bacteriology may now be said to constitute 

 almost an integral part of a liberal education, although, judging from the 

 flagrant inaccuracies which are to be found in the numerous references to 

 matters bacteriological in the daily press, it is evident that the news- 

 paper correspondents who undertake to inform the public on these topics 

 have not, as a rule, had the benefit of the liberal education in question. 



Perhaps the circumstance most calculated to impress the British 

 public with the present importance of bacteriology is that pure cultiva- 

 tions of micro-organisms have now for some years past become actually 

 articles of commerce. Not only are pure yeasts, prepared according to 

 Hansen's methods, in circulation all over the world, but pure cultivations 

 of pathogenic and other bacteria can now be purchased at catalogue 

 prices, to the great convenience of the investigator, in much the same way 

 as we have been in the habit of procuring pure and inaccessible chemicals 

 from Kahlbaum's. Again, bacterial poisons have been employed in 

 various parts of the world for combating animal plagues, whilst domesti- 

 cated bacteria have been used for the preventive inoculation of cattle and 

 other animals. 



If, however, the general methods of bacteriological study have under- 

 gone but little change recently, the greatly increased attention which 

 has been given to the study of particular forms isolated by these methods 

 has led to some important developments in our views concerning bacteria 

 in general. 



Although the discovery of the existence of micro-organisms was neces- 

 sarily made with the microscope, and the earlier information concerning 

 them obtained almost exclusively by means of this instrument, the intro- 

 duction of the modern bacteriological methods soon relegated the micro- 

 scope to a secondary position for the purpose of their differentiation and 

 diagnosis. It was early found that bacteria which were perfectly 

 undistinguishable when viewed through the microscope might exhibit tbi^ 

 most marked differences in their macroscopic appearances and in their 

 functions. Using the modern methods of bacteriological study, indeed, 

 the investigator generally becomes acquainted with such macroscopic 

 differences amongst micro-organisms before the microscope is brought 

 into requisition at all. It results from this that in examining any given 

 material the number of different bacteria discovered by cultivation 

 methods will generally greatly exceed that revealed by microscopic 

 examination alone. Upon the introduction of these cultivation methods 

 there rapidly followed, then, the discovery of a large number of different 

 kinds of bacteria obtained from the most varied sources, tissues healthy 

 and diseased, soil, water, air, &c. These different kinds of bacteria were 

 distinguished by more or less well-marked characters, e.g., the liquefaction 

 or non-liquefaction of gelatin, the appearances of the growths in various 

 culture media, the production of pigments, the pathogenic or non- 

 pathogenic properties on different animals, whilst in some cases the ability 



