VIROLOGICAL METHODS 247 



improvement, stunt the adaptation necessary when the test is apphed to 

 other than its original purpose, and encourage avidity for preciseness over 

 principle. In virology, as in other studies, standard technics make a 

 valuable contribution if used mth awareness of the purpose for which 

 they were designed and of their inherent hmitations and as a point of 

 departure or reference when the need arises. 



It is hoped rather that beginners may find herein some basic tools with 

 which to start. Application of each technic to specific diseases requires 

 space provided for in books but not in leaflets or sections. No apology is 

 offered for what must be redundant emphasis on caution and control. 

 Viology is a science based almost predominantly on indirect methodology. 

 One may work weeks with a virus without seeing it. Hence, caution and 

 control are extremely important. 



PRECAUTIONS 



Laboratory infections are not unknown among virologists. Many of 

 the viruses and rickettsiae isolated from man or animals are capable of 

 infecting man even after having been cultivated in the laboratory for a 

 long time. Perhaps the most rehable method for the novice is to train 

 under an experienced virologist. Nevertheless there are areas encom- 

 passing greater dangers than others. Generally speaking less hazard is 

 encountered when working with tissue cultures and embryonated eggs 

 than with laboratory animals. The use of adequate isolation quarters 

 for the animals and means for the worker to handle the animals without 

 coming in direct contact with them or their products (excrement, expired 

 air, etc.) is often mandatory while certain highly pathogenic viruses are 

 being investigated. 



Any material containing viruses or rickettsiae pathogenic for man must 

 be treated with respect. Any maneuver which tends to create an aerosol 

 presents a hazard. Grinding infected tissue with a mortar and pestle, 

 disintegration of infected tissue with a tissue blender or sonic vibrator, or 

 the simple acts of transfer or mixing with the pipet may produce danger- 

 ous aerosols. The use of special hoods and ventilating systems, where 

 possible aerosols may be moved, away from the operator and subse- 

 quently sterilized or diluted beyond danger, is important to safeguard the 

 worker. 



Large droplets caused by grinding or manipulating infected tissue may 

 be dealt with by placing a towel soaked in 1 per cent phenol on the table 

 top and placing receptacles and various pieces of equipment over it. 



Working in a gown or laboratory coat which can be readily removed and 

 sterilized is a worth-while practice. Washing the hands with soap and 

 water immediately after working with infectious material or at any time 



