EXAMINATION OF "FRESH" PREPARATIONS. 45 



little practice and careful observation, such errors may be left out 

 of court entirely. 



Examination of " Fresh " Preparations. 



31. Although up to the present we have considered the examination 

 of dried and stained specimens only, it will be readily understood that, 

 after all, such examinations are far from perfect, and that the appear- 

 ances during life and the chemical peculiarities can only be deter- 

 mined by a careful examination of the micro-organisms in the fluids 

 or tissues in which they are growing. Such an examination should 

 be made in all cases where motion of the object in question could 

 afford us any clue as to its nature. In blood, for instance, in which 

 septic bacilli (Pasteur) are supposed to be present, the spontaneous 

 movements of the bacillus will afford a most direct proof of its 

 vitality. By these spontaneous movements currents are set up, and 

 shifting of the positions of the corpuscles are brought about, even 

 when the organisms themselves are distinguishable only by the 

 exercise of the greatest care. 



Such movements are of even greater importance when we come to 

 the examination of bacteria cultivated in fluid media, for it is by 

 these that the organic nature of the growth in the fluid may be at 

 once determined. At the same time, as Naegeli points out, the move- 

 ment should be spontaneous to be of any very great diagnostic value, 

 and should be sharply differentiated from the oscillatory Brownian 

 movements, or from those movements brought about by currents 

 caused by evaporation, altered temperature, movements of the shde 

 or cover-glass, and other similar external causes. 



By far the simplest method for such fresh examination is to take a 

 drop of the germ-laden fluid, blood, meat broth, sugar solution, &c. in 

 a fine glass pipette, place it on a clean slide, put on a cover-glass, and 

 examine at once. The fluid is perfectly transparent, and nothing but 

 the well defined micro-organisms are seen, either alone or between 

 the blood corpuscles, or in or around other cells. Should there be 

 any tendency to dry, a drop of distilled water, or, still better, a drop 

 of three-quarter per cent, solution ol common salt, that has been 

 thoroughly sterilised by boiling, may be added. .By dropping such 



