Constituents of Thames Mud. By Lionel S. Beale. 15 



favourable conditions. The changes effected by them on the 

 products resulting from the death of man, the higher animals, 

 and plants, are, and probably have ever been, the same in their 

 essential nature at all times, but a longer time is required for the 

 completion of the changes in cold than in warm weather. 



Although chemical change, irrespective of the action of living 

 forms, and especially the action of oxygen, undoubtedly plays an 

 important part in the disintegration and reduction to simpler and 

 more stable compounds of some of the constituents of sewage, 

 particularly the excrementitious matters of the human body, by far 

 the most extensive changes, and those effected on the largest scale, 

 are brought about by these minute organisms. Bacteria are among 

 the lowest and simplest Hving forms in nature, and as I have men- 

 tioned are universally present, or at least are to be found wherever 

 moisture-laden air exists. Some forms of these bodies do not even 

 require oxygen for their subsistence. They can live in nitrogen, 

 carbonic acid, and probably in gases of the most poisonous and 

 deleterious character for a length of time, though they do not 

 grow and multiply quickly until conditions favourable to them are 

 established. 



In the present state of knowledge it is not possible to explain 

 precisely how these organisms act upon the offensive sewage 

 matter, but it is probable that as they grow and multiply they 

 actually feed upon and consume the noxious material. After 

 living its life the bacterium dies, and the products arising from its 

 decay and disintegration are harmless indeed as compared with 

 the substances upon which it has fed, and which for the most part 

 it is our great anxiety to be rid of. The matters resulting from 

 the disintegration of bacteria in turn become the food of plants. 

 If not taken up by vegetation these compounds would remain 

 passive as a soft brown granular material which is stable, and 

 undergoes scarcely any change whether it remains constantly 

 moist, as in mud, or sometimes dry and sometimes wet as the 

 humus of earth. Few organic substances undergo so little change 

 from century to century, nay, from age to age, as for instance 

 those products of plant decay which constitute the principal con- 

 stituents of various kinds of peat. The same may be said of the 

 last products of the decay of animal matter. For after the 

 offensive gases which characterize the ordinary putrefactive change 

 of animal matter have been evolved, and the putrefactive process 

 has run its course, slow evaporation takes place, and, after hundreds 

 and thousands of generations of bacteria have passed through the 

 several phases of existence and have died, there results a brown 

 substance which preserves its characters for centuries, and probably 

 undergoes no further change at ordinary temperatures. 



In the disintegration of the substances resulting from the death 



