14 



eveiT sample of air is sliown by the experiments before mentioned 

 of Tyndall opening sterilized flasks on the Alps. They are related 

 to dust. How long the adalt forms may survire in dry dnst is 

 not kno\ni, but the spores are much more enduring, hence in 

 cultivations from old dust we are not surprised to hear that only 

 spore-forming species are found (ftmgi, bacilli). In warm moist 

 rooms, according to Horsley, all forms are seen. The largest 

 numbers are found in the air in the neighbourhood of decomposing 

 substances. The atmosphere is also much purer in this respect in 

 rainy than in hot dry weather. Klein, and others, tell us that 

 the trouble in conducting sterilizing and cultivation experiments, 

 varies very greatly according to the state of the weather, and the 

 locality where the experiment is mads. Recent investigations 

 show that these organisms are found in the soil, but not below 

 the depth of one metre. They have probably been washed in by 

 water. Their presence or absence in water depends upon the 

 existence or otherwise of proper nutritive material in a suitable 

 state of concentration. In view of these facts Burdon Sanderson 

 has come to the conclusion that decomposing substances owe 

 their contamination more frequently to water than to air, but 

 this question is not yet settled. 



Gentlemen, the history of this subject reminds me somewhat 

 of the account of an arctic expedition. The journey dovna. the 

 river is easy enough, and the various odoure there encountered 

 might serve to link the two subjects together. The sea voyage at 

 first is extremely pleasant, but after a time our diflBculties begin, 

 and unfortunately they increase as we go on. I fear we are 

 nearing the ice. 



I will now ask you to turn your attention once more to the 

 infusions. If we place a drop fi-om one of these decomposing 

 liquids under the microscope we shall observe a number of living 

 forms scattered through it, such as torul* cells, fiTugus mycelium, 

 &c., but, besides these, some other very minute organisms, with 

 which we are at j^resent specially concerned. First of all we 

 shall notice a number of extremely minute spherical bodies, which 

 sometimes appear singly, more usually in pairs, looking somewhat 

 like a figure 8, and sometimes connected together in chains, or 

 branched forms, or aggregated into masses (zooglcea). These are 

 known as micro-cocci (little beads). Then there wiU be seen 



