8 MICRO-ORGANISMS AND DISEASE [chap. 



ascertain as far as possible the motility, chemical reactions, 

 and general morphology of living fresh specimens. Blood, 

 juices, tissues, and fluids in which the micro- organisms are 

 present, are subjected directly, without any previous prepa- 

 ration, to microscopic examination. In the case of artificial 

 media in which micro-organisms have been growing, the 

 examination of fresh specimens is of great importance, for 

 the reason that the organisms can be easily identified and 

 their size and general morphological characters be more 

 correctly ascertained than after drying, hardening, and 

 staining. Besides, the chemical reactions can be satisfac- 

 torily studied in fresh specimens only. All one has to do 

 is to draw up with a capillary pipette or to take up with the 

 point of a platinum needle a drop or particle of the mate- 

 rial, to place it on an object-glass, and to cover it up with a 

 thin cover-glass. Where one has to deal with liquids, such 

 as artificial nourishing fluids, blood serum, tissue-juices, 

 secretions, transudations and exudations, no addition is re- 

 quired. In the case of more solid material, such as solid 

 artificial nourishing material, bits of tissue, &c., the addition 

 of a drop of neutral previously well-boiled saline solution 

 (of o'6 to 075 per cent.) is advantageous although not 

 absolutely necessary, since by pressing down the cover-glass 

 a layer of the material sufficiently thin for examination can 

 be obtained. In some instances a bit of tissue can be 

 teased out into fine particles by means of two clean 

 needles. Where it is a question of micro-organisms suffi- 

 ciently conspicuous by their shape, size, and general appear- 

 ance, their identification in the fresh condition is not 

 difficult ; this is the case with bacilli, vibrios, actinomyces, 

 and mycelia, but in the case of micrococci, especially when 

 isolated or in couples, and lying in blood, juices, or tissues, 

 their recognition is often extremely difficult. When in large 



