148 Transactions. — Miscellaneous. 



tage is taken in this system of the fact that certain very power- 

 ful liquefying organisms only exist and act in the absence of 

 air. For this reason the tank is closed hermetically, and the 

 inflow and outflow pipes dip under the fluid-level and prevent 

 ingress of air. All organic solids are liquefied in this chamber. 

 The nitrifying organisms soon grow in the filter-beds, which 

 are freely exposed, and the solution of ammoniacal and re- 

 duced organic products is nitrified and oxidized in the passage 

 through the coke. When possible the effluent can be applied 

 with advantage to the land, as it is rich in nitrates and other 

 useful manurial salts. But if land is not available it can flow 

 into the sea or stream without fear of offence. 



Here, then, we use Nature's own processes, chained up, as 

 it were, and w 7 orking for us at our bidding, and as a result we 

 have in this system the nearest approach to perfection yet 

 attained in sewage treatment. 



■ s - 



Protection. 



I must now briefly mention another law by which Nature 

 protects the public health, a law which is of interest from the 

 fact that it is at work in our own bodies, enabling us to fight 

 against the inroads of disease germs. There is a natural 

 resistance of the living body against organisms which attack 

 it. The living animal cell and the disease germ or pathogenic 

 bacterium are engaged in a continual warfare. Probably the 

 general health of the body has much influence on the question 

 of which way the warfare will end, since we know that influ- 

 ences tending to depress the general health also tend to lay 

 the body open to attack by such infective organisms. We 

 know, for instance, that persons living in unwholesome sur- 

 roundings are more liable to attacks of typhoid fever than 

 those whose environment is sanitary, and this has been 

 demonstrated experimentally with guinea-pigs. Anything 

 tending to depress the vitality of the living cell favours the 

 infective germ by lessening the resistance. 



But Nature has another beautiful law of compensation, a 

 law by which she makes the very life of the germ prove 

 antagonistic to itself. It is the law which confers on us 

 immunity from second attacks of an infectious disease. We 

 all know that second attacks of scarlet fever, typhoid, small- 

 pox, and so on, are rare. If it were not so, if there were no 

 such thing as acquired immunity from such diseases, and we 

 were to catch them as frequently as we catch cold, life would 

 be a pretty serious matter. The secret of how Nature works 

 this law has been an object of speculation with scientists for a 

 long time, and we are now beginning to have some glimmer- 

 ing of light on the subject. 



