Bacteria count among the solid particles as well as the bacteriophage found in bacteria cultures, lastly viruses. All these germs can be present in compressed air either as floating particles or cling to solid or liquid particles.
As a rule, germs adhere to dust particles. Increase in dust particles leads to a higher germ content. In traffic arteries, an average enrichment in germs of up to 10 000/m3 was noted. Germs are living organisms of plant or animal origin, as well as microbes, bacteria and micro organisms in spherical, cylindrical, spiral or thread form, which propagate extremely fast through splitting. Some of these germs cause dangerous infections, others, on the other hand, cause putrefaction or fermentation. Only a very small.portion of the germs cause infections.
Most germs quickly die when drying and, therefore, infection through the air is relatively rare. Infection takes place almost exclusively through droplets which are finely spread in the air through coughing or sneezing. Bacteriophage and viruses, both of approximately the same size, have a diameter of only 0.003 - 0.3 µm, they are thus 100 times smaller than bacteria. Foot and mouth disease virus belongs to the smallest viruses whereas the smallpox virus is among the largest. Whereas bacteriophage can be found as parasites in bacteria cultures where they virtually devour the bacteria, viruses as a rule cause infections of more or less noxious character.
Viruses cause illnesses such as influenza or measles in the human body. Bacteria, on the other hand, are the cause of many infectious diseases such as diphtheria, tuberculosis or cholera. Bacteria in the widest sense have a size of about 0.2 - 30 µm. Actinomyces (ray fungi) count among the bacteria, then the bacteria in the narrower sense known through propagation by splitting, furthermore the spore forming bacilli, the spherical cocci as well as the helical spirils and spirochetes, finally the comma shaped vibrios which move about through a whipping motion and which cause cholera. Bacteria are omnipresent but must, at all cost, be kept away from certain products. For instance, when vaccines are produced, germs causing infection must not be present in the breathing air.
All these germs are very insensitive to cold and dryness. It is only heat, approaching boiling point, which they cannot withstand. If, at the same time, there is sufficient nutriment, germs multiply particularly fast in the presence of moisture. Anaerobic bacteria, however, only multiply and survive when there is no oxygen present. Viruses generally multiply only within the host body.
