tion of slides, plating of cultures, the pouring of microbial suspen sions, and pipetting. These procedures can be serious sources of infection if a hazardous pathogen is being handled. Each of these actions will be discussed individually. For individuals whose body defenses are compromised by underlying disease or medical treat ment, it is sensible for them to check with their physician as to the potential hazards to them of working in a microbiology lab where even organisms that are normally nonpathogenic are being handled The Inoculating Loop Excessively long or improperly made loops can shed their inoculum, either by vibration or spontaneously. A film formed by a loopful of broth culture that is vibrated can break the surface tension that keeps the film in place, forming an aerosol. The longer the loop is, the more vibration that ensues from handling An incompletely closed loop can also easily result in a break in surface tension of the film. The optimal size of loop is approxi mately 2 to 3 mm in diameter, and the loop should be completely closed. The length of the wire portion of the loop, or shank, should be approximately 5 to 6cm. If a large flask is being inoculated tilting the flask to bring the liquid closer to the neck may be a way to avoid the use of a very long wire. When loops become excessively bent or encrusted with carbonized material, they should be replaced. Pre-sterilized, single-use plastic loops are also available. They are not to be placed in contact with flame or solvents such as acetone and should be discarded into a disinfec tant solution The discharge of proteinaceous or liquid material that often follows flaming a loop has been suspected as a source of contam- ination, but there is little evidence to support this contention Nonetheless, it is best to decontaminate the wire loop by placing it into the apex of the internal blue flame of the burner so that any discharged material has to pass through the bulk of the flame as it leaves the loop. Preparation of slid The production of aerosols by spreading of a bacterial suspension on a slide is minimized by gentle movements, espe cially when removing the loop from the spread suspension For pathogens this activity is best performed in a biosafety hood, and the slides should not be removed from the hood until completely dried Working Safely with Biological Samples 12tion of slides, plating of cultures, the pouring of microbial suspen￾sions, and pipetting. These procedures can be serious sources of infection if a hazardous pathogen is being handled. Each of these actions will be discussed individually. For individuals whose body defenses are compromised by underlying disease or medical treat￾ment, it is sensible for them to check with their physician as to the potential hazards to them of working in a microbiology lab where even organisms that are normally nonpathogenic are being handled. The Inoculating Loop Excessively long or improperly made loops can shed their inoculum, either by vibration or spontaneously. A film formed by a loopful of broth culture that is vibrated can break the surface tension that keeps the film in place, forming an aerosol. The longer the loop is, the more vibration that ensues from handling. An incompletely closed loop can also easily result in a break in surface tension of the film. The optimal size of loop is approxi￾mately 2 to 3 mm in diameter, and the loop should be completely closed.The length of the wire portion of the loop, or shank, should be approximately 5 to 6 cm. If a large flask is being inoculated, tilting the flask to bring the liquid closer to the neck may be a way to avoid the use of a very long wire. When loops become excessively bent or encrusted with carbonized material, they should be replaced. Pre-sterilized, single-use plastic loops are also available. They are not to be placed in contact with flame or solvents such as acetone, and should be discarded into a disinfec￾tant solution. The discharge of proteinaceous or liquid material that often follows flaming a loop has been suspected as a source of contam￾ination, but there is little evidence to support this contention. Nonetheless, it is best to decontaminate the wire loop by placing it into the apex of the internal blue flame of the burner so that any discharged material has to pass through the bulk of the flame as it leaves the loop. Preparation of Slides The production of aerosols by spreading of a bacterial suspension on a slide is minimized by gentle movements, espe￾cially when removing the loop from the spread suspension. For pathogens this activity is best performed in a biosafety hood, and the slides should not be removed from the hood until completely dried. Working Safely with Biological Samples 121