90 AN INTRODUCTION TO THE STUDY OF VIRUSES 
5. Measures of General Hygiene 
Included in this category are the obvious routine precautions of 
isolation and quarantine which reduce to a minimum the contact 
between the diseased and healthy subject. In the cases of influenza 
and the common cold it is hardly necessary to point out the danger of 
unrestrained sneezing and coughing. The droplets from a sneeze 
remain suspended in the air for more than ten minutes. A large 
handkerchief carefully used prevents the scattering of these droplets 
and a simple impermeable mask collects the vast majority of them. 
The use of the hand for checking such scattering is ae inefficient 
(Bourdillon and Lidwell, 1941). 
Apart from this more obvious method of sehGnae infection of 
comparatively large droplets, attention is now being directed to the 
possible spread of these two viruses on dust and in a more or less dry 
condition. It has been demonstrated (Edward, 1941) that, after 
impregnation of a blanket with a suspension of influenza virus, the 
virus survives drying under ordinary atmospheric conditions and can 
be distributed in the air on dust particles by shaking the blanket. 
It was also found that the virus would withstand drying on a variety 
of other materials including household dust. The time for which the 
virus remained active was also estimated. There was little depreciation 
after 3 days, 10 per cent might persist for a week, and 1 per cent for 
a fortnight. Disappearance of the virus was much more rapid when 
impregnated material was kept at 37°C or in the light. Recent work 
of C. H. Andrewes and his collaborators on the common cold virus 
suggests that spread may take place through this virus being shaken 
out of handkerchiefs, especially when the latter have been used in the 
later stages of a cold. The possibility is suggested that impregnation 
of handkerchiefs with a disinfectant might make them less dangerous 
in this respect. 
Some cheap and efficient method of destroying bacteria and virus 
particles in the air is badly needed. A sodium hypochlorite mist is 
fairly effective (Andrewes et al., 1940) and ultra-violet light is useful 
under certain circumstances, but too expensive. 
Virus Diseases of Plants 
There are various methods for the control of plant virus diseases 
and there are two main avenues of approach to the problem. The first 
is to ward off, or avoid exposing the plant to, infection, and the second 
