Practical bacteriology, microbiology and serum therapy (medical and veterinary) : a text book for laboratory use / by A. Besson ; translated and adapted from the fifth French edition by H.J. Hutchens.

Besson, Albert, 1868-

Date:: 1913

Credit: Practical bacteriology, microbiology and serum therapy (medical and veterinary) : a text book for laboratory use / by A. Besson ; translated and adapted from the fifth French edition by H.J. Hutchens. Source: Wellcome Collection.

886/928 (page 854)

$No account is taken of the presence of anaerobic organisms in stating the number present in a water : the determination is always made under aerobic conditions and this is always tacitly understood. By employing anaerobic methods of isolation the number of anaerobic organisms could of course be determined, but in practice this is never done, and it presents difficulties other than those of technique—such for instance as the occurrence of facultative anaerobes, many of which, as a matter of fact, grow on the aerobic plates. Vincent investigated the occurrence of anaerobic organisms in water and found that the number of strictly anaerobic organisms was very small. He used Vigna-l’s tubes and glucose-gelatin, containing sulphindigotate of sodium (p. 92). The medium was sown by the dilution method, and for the detection of pathogenic species the colonies so isolated were sub-cultivated anaerobically in broth and then inoculated into animals (p. 858). In determining the number of organisms in an unit volume of water it is usual to work with a fraction of a cubic centimetre because the number of organisms present in a cubic centimetre is generally so large as to make an enumeration impossible. A. Dilution method.—1. Chip away the wax with which the cork was sealed and flame the top of the cork in a Bunsen : raise the cork with a flamed corkscrew sufficiently to allow of it being removed from the bottle with the fingers.1 2. Have ready on the bench :— A 10 c.c. pipette graduated in 1 c.c. A 2 c.c. pipette graduated in 05 c.c. A drop pipette (20 drops to 1 c.c.). (All of which must, of course, have been plugged with wool at the upper end and steri- lized.) A sterile glass vessel covered with paper. A tube of sterile water. Several tubes of sterile gelatin in a water bath at a temperature high enough to keep the medium fluid. Several conical flasks plugged with wool and sterilized (fig. 408). 8. Into the sterile glass vessel measure 9 c.c. of sterile water adopting all precautions to avoid contamination : add 1 c.c. of the water under examina- tion and mix thoroughly. This gives a dilution of 1 in 10. 4. Flame the mouth of one of the conical flasks, remove the wool plug and with the drop pipette introduce 2 drops of the 1-10 dilution of the water ( = 0-01 c.c.). 5. Flame the mouth of one of the tubes of liquefied gelatin (the tempera- ture of which should be such that the tube can be held quite comfortably in the hand), remove the plug and pour the contents quickly into the conical flask (par. 4). Replace the wool plug in the mouth of the flask, mix the gelatin and water thoroughly by rotating the flask and then stand the latter on some cold and horizontal surface so that the gelatin may set as quickly as possible. In effect, plate O01 c.c. of the water on gelatin. 6- Incubate at 20°-22°C.] 7. Colonies will soon appear in the gelatin, each colony representing one 1 Before uncorking the bottle shake it well to mix thoroughly the contents and to dis- tribute any deposit there may be uniformly throughout the whole. Fig. 408.—Conical flask (Gayon’s)$