. Laboratory work in bacteriology. Bacteriology. 514. BACTEKIOLOGY. each germ present should be sing'le and wholly free from contact with other organisms. The massing of bacteria necessarily affords protec- tion to the cells in the center of such groups. Because of this protec- tion these few cells may survive, while all the others may be destroyed. The results obtained would consequently be misleading. This error can be avoided by filtering the suspension through sterile absorbent cotton or glass-wool in the manner presently to be described. When it is desired to test the resistance of the ve
. Laboratory work in bacteriology. Bacteriology. 514. BACTEKIOLOGY. each germ present should be sing'le and wholly free from contact with other organisms. The massing of bacteria necessarily affords protec- tion to the cells in the center of such groups. Because of this protec- tion these few cells may survive, while all the others may be destroyed. The results obtained would consequently be misleading. This error can be avoided by filtering the suspension through sterile absorbent cotton or glass-wool in the manner presently to be described. When it is desired to test the resistance of the veg^eta- tive form of a given organism special care must be taken to exclude the presence of spores. Many bacteria like those of typhoid fever, cholera, etc., do not form spores and hence such precautions are not observed when testing these organisms. The anthrax bacillus, however, does form spores, and hence in testing the resist- ance of the growing bacillus the spore form must be eliminated. This is ac- complished by making so-called homo- geneous cultures. These are obtained by making transplantations to bouillon every 6 or 8 hours. After several such transplantations only actively growing bacteria will be present. The best procedure for studying the Fig. 74. Filter for bacterial action of moist heat on bacteria, is to suspensions. place homogeucous suspensions in thin, straight capillary tubes. It is essential that the walls of the capillary tube shall be as thin as possible. They should not have a bulb of thick glass. When such sealed capillary tubes are immersed they rapidly acquire the tem- perature of the surrounding liquid. Preparation of a bacterial suspension.—As a rule, it is best to era- ploy young cultures on agar. Sterile bouillon is introduced into the test-tube by means of a drawn-out pipette (Fig. 61 e) and the growth is thoroughly rubbed up. The suspension is now drawn up into the pipette and is transferred to a sterile filter (Fig. 74), The filter-tube. Ple
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