248 SCIENCE FROM AN EASY CHAIR 



renders it worth investigating the question as to whether 

 there are " local " germs or microbes which in this or that 

 region are abundant and get into man's food and drink, 

 and so into his intestine, and become established there, 

 helping or antagonising the growth of other microbes 

 already there or subsequently introduced. Thus, to the 

 various considerations in regard to the " air " of a locality, 

 such as rarefaction, moisture, temperature, movement, 

 ozone, and the perfumes and exhalations of pine trees, 

 rosemary, and sweet-smelling grasses, which seem to be 

 those which are the most likely to affect the health of 

 inhabitants and visitors, it is not improbable that we must 

 add the influence of an invisible local flora of microbes. 

 The inquiry is a long and laborious one, but it will be 

 carried through. The microbes, whether in air or water, 

 or on the surfaces of things, can be collected by washing 

 them into warm liquid gelatine. Then the gelatine is 

 poured out on a plate, and hardens as a thin sheet of jelly. 

 This is protected from all further contamination, and, 

 after a few hours, each invisible microbe embedded im- 

 movably in the jelly makes itself apparent. It multiplies 

 enormously whilst remaining stuck to one spot, and is no 

 longer invisible, but presents itself to the eye as a little 

 sphere, or disc, of characteristic shape, colour, and quality, 

 consisting of many hundred thousands of crowded 

 microbes produced by the growth and division of the 

 original invisible one. Some dozens or some hundreds of 

 little growing " dots," and of many various kinds, will thus 

 reveal themselves in the jelly according to the number and 

 kinds of utterly invisible parent microbes introduced by 

 your " washings" into the jelly. And so the investigator 

 has the means of getting at each kind of invisible microbe 

 quite detached from the others, and of separating it for 

 further cultivation and experiment as to its chemical and 

 disease-producing qualities. These microbial gardens of 



