212 president's address. 



of individuals being 4,772 billions. It is fortunate that ^ the 

 conditions favourable to such extremely rapid development are 

 rarely or never found. Still, it would be a mistake to look upon 

 Bacteria as altogether noxious beings. They are indeed the great 

 scavengers of nature, seizing speedily upon dead and effete mate- 

 rial, and by the various fermentive and putrefactive processes 

 which they set up reducing the highly complex constituents of 

 organic beings to their primitive inorganic elements. Without 

 the help of bacteria it would seem impossible that the cyclical 

 changes inseparable from the course of nature could go on — 

 that there could be that never-ceasing decay and rejuvenescence 

 which are inseparable from life itself. This has been put very 

 emphatically by Duclaux : ' whenever and wherever there is 

 decomposition of organic matter, whether it be the case of a 

 herb or an oak, of a worm or a whale, the work is exclusively 

 done by infinitely small organisms. They are the important, 

 almost the only, agents of universal hygiene ; they clear away 

 more quickly than the dogs of Constantinople or the wild beasts 

 of the desert the remains of all that has had life ; they protect 

 the living against the dead ; they do more : if there are still 

 living beings, if, since the hundreds of centuries the world has 

 been inhabited, life continues, it is to them we owe it."*' 



To make sure that the Bacteria found in any particular disease 

 are the actual cause of it, it is necessary to separate the suspected 

 species from all others, — for many forms are often found living 

 together — to cultivate it, and by inserting these cultivations 

 into the body of some animal, to ascertain whether the disease 

 in question can be so produced. And it is only within quite 

 recent years that we have been enabled to fulfil these require- 

 ments. To avoid sources of error which would be constantly 

 arising by the entrance of germs from the external air, it is 

 indispensable that the apparatus and material used should be 

 sterilised by boiling or by other exposure to sufficient heat, and 

 cf course that all tubes or apertures leading into the air should 

 for the same reason be hermetically sealed or sufficiently plugged. 

 Several methods of cultivation are in use, but the most general 



* Woodhead : Bacteria and their Producte, pp, 68, 6a, 



