RECOGNITION OF MICROORGANISMS. 27 



they should be allowed to remain for several minutes, then transfer 

 to ether or chloroform in a watch-glass, and 'afterwards to a strong 

 solution of acetic . acid. Wash thoroughly in distilled water, after 

 which the sections may be warmed gently (until bubbles begin to 

 rise) in a two per cent, solution of caustic potash. By this treatment 

 all fat granules, which may be mistaken for micrococci, all small 

 crystals, which are sometimes mistaken for bacilli, granular fibrin, 

 and even differentiation of structure, are removed, and only the 

 resistant groups or strings of micrococci or bacilli are left for examina- 

 tion. Where micro-organisms are present in large masses in vessels 

 or connective-tissue spaces, this method is extremely useful ; but for 

 single bacteria it is naturally far from satisfactory. If, however, the 

 single organism is in the form of a bacillus, it may be recognised by 

 its characteristic form, as the only thing for which it can be readily 

 mistaken, the fat crystal, has been removed by the above treatment. 



Recognition of Micro-Organisms. 



23. In the case of micrococci, the chemical reactions are most impor- 

 tant, but there are also certain points to which attention must be paid 

 in regard to evidence of growth, community of form, and size arid 

 regularity of arrangement, any or all of which may prove of great 

 service in helping to determine the nature of suspected granules. 

 Most experts agree that the forms of single micro-organisms render 

 but little help to the observer who has to determine their exact 

 nature. But these forms, when considered along with other fea- 

 tures, may prove of great value. Thus, when associated with a 

 sharp margin, a well defined outline, a high refractive index — giving 

 it a peculiar glistening appearance — the micro-organism is readily 

 enough recognised. The above refers especially to single cocci, but 

 other characteristics come to our assistance if these small bodies are 

 in groups. For instance, massed together, they have a peculiar brown 

 tinge, and, examining the individual cocci of which this mass is com- 

 posed, they are found to have all the above characteristics as to form, 

 outline, and appearance ; but then another striking feature attracts 

 attention — all the cocci of the same group are of equal size and are of 

 the same form. If, instead of large groups, small numbers of these 



