EXPERIMENTS ON MOTILITY 



155 



has passed through the porous walls of the bougie. Only motile organisms 

 can do this, and of these the typhoid bacillus is one of the first to pass through. 

 In attempting the isolation of the typhoid bacillus from water, the broth in 

 the bougie would be sown with some of the suspected water, and when the 

 broth surrounding it became cloudy a small quantity would be removed for 

 the purposes of further investigation by the usual methods (Chap. XXIII. ). 



B. Carnot and Gamier conceived the idea of making motile organisms 

 pass by their own efforts through a layer of sand of known thick- 

 ness, and then collecting the first organisms to pass through ; 

 they were thus able to determine exactly the time required by 

 a given organism to make its way through a given thickness of 

 sand. The degree of motility possessed by any species of micro- 

 organism can by these means be exactly measured. 



Technique. 1. A piece of glass tubing, 7 mm. calibre, is 

 drawn out in the flame about its middle, and bent into an 

 U -shape with the two limbs parallel and closely applied to each 

 other, each being about 25 cm. long (fig. 128). 



2. A loosely-packed plug of glass wool C is pushed down the 

 limb A as far as the constriction in the lower part. Broth is 

 then poured in to a depth of about 10 cm. in each tube. Very 

 fine quartz sand (previously washed in hydrochloric acid for 

 48 hours, and then in water for several days and afterwards 

 calcined in the hot air sterilizer) is slowly dropped down the 

 tube A until it forms a column 10-15 cm. high. A and B are 

 then plugged with wool, and the tube autoclaved. 



3. The organism whose motility is to be investigated is then 

 sown in the broth contained in the limb B in which there is 

 no sand, and the tube incubated at 37 C. The passage of 

 organisms through the sand is made manifest by a cloudiness 



of the broth in A. Only motile organisms reach the broth in A, and the time 

 occupied varies with different species. 



Carnot and Garnier give the following times for the most motile organisms : 

 Vibrio cholerse (Massaouah) traverses 1 c.c. of sand in 1 hr. 38 m. 

 ,, (Dantzig) , 2 hrs. 4 m. 



FIG. 128. 



(Paris, 1884) 

 Bacillus psittacosis 

 Bacillus febris entericae 

 Bacillus coli communis 



4 hrs. 



2 hrs. 



3-6 hrs. 



(variable, 1 hr. to 



several days). 



Streptococci with feeble undulatory movements, 4 hrs. 50 m. 



Bacillus anthracis, Staphylococcus pyogenes, Pneumococcus, etc., do not pass through 

 the sand. 



This method like that of Cambier may be utilized for the isolation of 

 motile organisms ; moreover it renders possible, by successive passages 

 of selected organisms, the creation of strains of a given bacillus possessed of 

 exceptional motility. In this way Carnot and Garnier were able after five 

 passages to isolate from a culture of the typhoid bacillus, which originally 

 took 6 hours to traverse a centimetre of sand, a strain which passed through 

 the same thickness in 1 hour and 4 minutes. 



