LECTURES. 39 



no effect on rats, fowls, frogs, white mice or the carnivora. Glanders, 

 though fatal to man, to the horse, to guinea-pigs, and to field mice, 

 has no effect on cattle, house mice, rabbits or pigs. 



To the question where do these all powerful, almost invisible, 

 organisms dwell, the answer is everywhere. In earth, air and water 

 they are equally at home. In the air they appear to be borne along 

 like seeds or motes. Far out to sea but few are found, and none or 

 next to none at the highest altitudes. Sunshine has a destructive 

 effect even on the spores of certain bacteria. By six or seven hours 

 exposure cholera bacilli were entirely destroyed, and the effects of 

 sunshine was found to penetrate some five or six feet of clear water. 

 It is thus that the germs of disease are destroyed in vast numbers by 

 exposure to the action of those powerful disinfectants, the wind and 

 the sun. 



In water and liquids of all kinds microbes thrive. Fortunately 

 for us it appears difficult for them to leave this element and pass into 

 the air. In twenty drops of unfiltered Thames water Dr. Frankland 

 found about 20,000 microbes, and when filtered there were 400. They 

 abound most in winter from the access of surface water and the 

 absence of sun. 



Our only safety lies in a pure source of our water supply, but 

 boiling does much for bad or doubtful water or milk. Filters of the 

 old type are worse than useless for the charcoal in them forms a 

 convenient breeding ground for the microbe. 



In the earth, bacteria are most active and vigorous — it has 

 probably been the original home of most varieties even of those now 

 parasitic in the .bodies of living animals. The lockjaw bacillus has 

 been found in mangrove swamps, whence it is obtained by the South 

 Sea Islanders, who dip their poisoned arrows in the water in which it 

 abounds. It is also present in garden soil and gutters and its wide 

 distribution should make us careful in the cleansing of any wound. 

 There are also living in the earth the useful microbes who carry on 

 their work of putrefaction even deep down in the dark. 



The remaining home of the microbe is the body of some living 

 animal, which they enter by the breath, or with the food, or by some 

 injured surface. 



Some kinds seem always with us, eight or ten ' species are 

 constantly to be found in the mouth, one of which has a digestive 

 power, and attacks the teeth, especially when the enamel has been 

 injured by acids. The best antidote for this one is a good tooth 

 brush, to be apphed frequently. 



