50 MICRO-ORGANISMS AND DISEASE. [CHAP. 



Spiller's purple, gentian violet, methyl blue, or magenta, 

 washing with water, then spirit, then distilled water, then 

 drying, and finally mounting it in Canada-balsam solution. 

 (c) Test-tubes containing sterile nourishing material (broth, 

 Agar-Agar mixture, gelatine mixture, Cohn's or Pasteur's 

 fluid) are inoculated in the manner described previously, i.e. 

 by piercing the cotton-wool plug with the pointed end of the 

 capillary pipette. These test-tubes are then exposed in the 

 incubator, and after one or two days or more, a sample is 

 withdrawn with a capillary pipette, and used for microscopic 

 examination. As a rule, after a day or two of incubation we 

 can already distinguish with the unaided eye whether there 

 are any organisms present, the nourishing fluid either being 

 uniformly turbid this is generally the case or there being 

 a growth at the bottom of the fluid. But of course the 

 microscopic examination only shows what kind of organisms 

 are present. New cultivations are made from this one, if any 

 are required, (d) A good plan of recognising easily that 

 there are present various kinds of organisms in such cultures 

 is one similar to that recommended by Professor Angus 

 Smith. 1 Sterile gelatine broth or gelatine only, contained in 

 sterile test-tubes plugged with sterile cotton-wool, is liquefied, 

 but of course not heated to more than about 35 to 40 C. 

 then inoculated with the water (to be tested), by means of 

 the capillary pipette ; after inoculation the gelatine is mixed 

 by shaking the test-tube slightly. In this way the organisms 

 present in the water are distributed in the gelatine. Then 

 the gelatine is allowed to set and is kept in this solid state. 

 The organisms being distributed in the gelatine, after some 

 days' growth are noticeable as clusters which gradually 

 increase in extent and are distributed in various parts of the 



1 Sanitary Record, p. 344, 1883. 



