544 FRAGMENTS OF SCIRNCE. 



it will remain forever sweet. Thus we begin to see that 

 within the world of life to which we ourselves belong, 

 there is another living world requiring the microscope for 

 its discernment, but which, nevertheless, has the most 

 important bearing on the welfare of the higher life- 

 world. 



And now let us reason together as regards the origin of 

 these bacteria. A granular powder is placed in your hands, 

 and you are asked to state what it is. You examine it, and 

 have, or have not, reason to suspect that seeds of some 

 kind are mixed up in it. To determine this point you 

 prepare a bed in your garden, sow in it the powder, and 

 soon after find a mixed crop of docks and thistles sprout- 

 ing from your bed. Until this powder was sown neither 

 docks nor thistles ever made their appearance in your 

 garden. You repeat the experiment once, twice, ten times, 

 fifty times. From fifty different beds after the sowing of 

 the powder, you obtain the same crop. What will be your 

 response to the question proposed to you? " I am not in 

 a condition," you would say, " to affirm that every grain 

 of the powder is a dock-seed, or a thistle-seed; but I am in 

 a condition to affirm that both dock and thistle-seeds form, 

 at all events, part of the powder." Supposing a succession 

 of such powders to be placed in your hands with grains 

 becoming gradually smaller, until they dwindle to the size 

 of impalpable dust particles; assuming that you treat them 

 all in the same way, and that from every one of them in a 

 few days you obtain a definite crop it may be clover, it 

 may be mustard, it may be mignonette, it may be a plant 

 more minute than any of these, the smallness of the par- 

 ticles, or of the plants that spring from them, does not 

 affect the validity of the conclusion. Without a shadow 

 of misgiving you would conclude that the powder must 

 have contained the seeds or germs of the life observed. 

 There is not in the range of physical science an experi- 

 ment more conclusive nor an inference safer than this one. 



Supposing the powder to be light enough to float in the 

 air, and that you are enabled to see it there just as plainly 

 as you saw the heavier powder in the palm of your hand. 

 If the dust sown by the air instead of by the hand 

 produce a definite living crop, with the same logical 

 rigor you would conclude that the germs of this crop 

 must be mixed with the dust. To take an illustration: 



