EXAMINATION OF LIVING ORGANISMS 127 



Although the modern methods of isolation and cultivation have 

 rendered immense service to bacteriology, they have also had the 

 effect of diminishing the attention paid to the exact morphology 

 and biology of organisms. At the present time there is a tendency 

 to investigate bacteria en masse rather than to study them as 

 individual living forms. As the late Marshall Ward remarked : 



" The introduction and gradual specialisation of Koch's method 

 of rapid isolation of colonies encouraged the very dangers they were 

 primarily intended to avoid. It was soon discovered that pure 

 cultures could be obtained so readily that the characteristic differ- 

 ences of the colonies in the mass could presumably be made use of 

 for diagnostic purposes, and a school of bacteriologists arose who 

 no longer thought it necessary to patiently follow the behaviour of 

 the single spore or bacillus under the microscope, but regarded it 

 as sufficient to describe the form, colour, markings, and physiological 

 changes of the bacterial colonies themselves on and in different 

 media, and were content to remove specimens occasionally, dry and 

 stain them, and describe their forms and sizes as they appeared 

 under these conditions. To the botanist, and from the point of 

 view of scientific morphology, this mode of procedure may be 

 compared to what would happen if we were to frame our notions 

 of species of oak or beech according to their behaviour in pure 

 forests, or of grass or clover according to the appearance of the 

 fields and prairies composed more or less entirely of it, or and this 

 is a more apt comparison, because we can obtain colonies as pure 

 as those of the bacteriologist of a mould fungus according to the 

 shape, size, and colour, etc., of the patches which grow on bread, 

 jam, gelatine, and so forth." 



Examination of Living Organisms 



One essential procedure in the investigation of an 

 organism is its examination in the fresh and living con- 

 dition. This may be done by placing a droplet of sterile 

 water, broth, or salt solution on the slide, inoculating 

 with a trace of the material or growth, and covering 

 with a cover-glass and examining microscopically. The 

 action of stains and reagents on the organisms may be 

 observed by the irrigation method. A drop of the stain 

 or reagent (c, Fig. 21) is placed on the slide, A, just in 



