142 Transactions. — Miscellaneous. 



group of workers. Later another variety of fly appears, 

 which also feeds on the fatty matters ; these are the small 

 flies which we find in cheese. The next contingent are very 

 minute insects — the mites— whose work tends to dry up and 

 mummify the now highly decomposed body. This prepares it 

 for a further set of mechanics, whose food is found in the dried 

 skin and ligaments ; these are certain moths and beetles. 

 Finally a variety of beetle sets to work to utilise all the debris 

 left by the other squad of scavengers, working it into the soil 

 and tidying it all up. These insects appear in regular routine, 

 and do the grosser part of the clearing process. 



The Microbe. 



But the principal force making for the reduction of the 

 complex mass of material is the microbe. The process of 

 putrefaction by which organic matter — animal or vegetable — 

 is broken down and dissolved is produced by bacterial life. 

 And we are entirely dependent on the bacteria for the condi- 

 tions necessarv for existence, for if thev were absent organic 

 matter would not decay, plants could not live, and food- 

 supply would cease. These micro-organisms require for their 

 life, moisture, certain salts, and nitrogen and carbon in some 

 form, varying with the variety of the bacteria. One group 

 derive their nitrogen and carbon from the breaking-down of 

 already organized material, and others do so from the simplest 

 elements, building them up into the complex materials of 

 which their own bodies are composed. Thus it would not be 

 supposed that distilled water contained the elements of life 

 even for bacteria. Yet one variety will grow in it, deriving 

 its nitrogen and carbon from impurities in the air, such as 

 carbonic acid and ammonia. But it is the first or breaking- 

 down group which causes decomposition. An important 

 feature of this process is that the bacteria which cause disease 

 and death do not themselves long survive the decay which 

 then sets in. The putrefactive organisms are antagonistic to 

 them, and in course of time they disappear. Doubtless some 

 survive in a modified form when conditions are favourable, 

 and lie dormant awaiting an opportunity to again assert them- 

 selves ; but thorough exposure to air and light, combined with 

 the antagonism of the putrefactive organisms, and those uni- 

 versally present in earth and water, serve to kill out most 

 disease-producing germs. 



Inquiring now as to the agency by which these bacteria 

 produce their solvent effect, we find that the growth of 

 bacteria is accompanied by the production of heat — as in a 

 mass of wet hay — and of certain ferments, which are the 

 active chemical agents. If we filter a fluid in which these 

 germs are growing through porcelain we can separate the 



