264 BOARD OF AGRICULTURE. 



of simpler organization than the mould or yeast plant we 

 have described before. In fact, they are so very, very 

 minute they require the very best microscope that can be 

 made to study them at all. They are so small that 200,000,- 

 000 of them could move about (with a little crowding) in 

 a square inch surface. Let us see if we can determine 

 where these minute bodies came from. We will take the 

 three glass tubes again, and into them put a little water, and 

 also into each a small piece of meat. (Illustration.) Into 

 the mouths of two of the tubes we will put the cotton plugs, 

 and place all three in a hot oven until we have destroyed 

 any kind of life 'that may be in the tubes, and then set them 

 away in a warm room, 



In a few days we examine them, when we find the meat in 

 the open tube has commenced to undergo a change. AVe put 

 a little of it under the microscope, when we see millions of 

 those minute bodies in active motion, while the meat in the 

 other tubes has remained unchanged, Xow we will remove 

 the cotton plug from one of the tubes for a single moment, 

 and then replace it, and in a few days we find the meat in 

 this tube decomposing, for when we removed the cotton we 

 allowed some of the unfiltered air to enter the tube, carr3'ing 

 with it some of the germs of this fonu of life we have just 

 seen on the screen ; frilling upon the meat they at once begin 

 to groAv, reproducing themselves with astonishing rapidity. 

 These little bodies are called bacteria. As we have seen 

 that the growth of the 3'east plant is the cause of fermenta- 

 tion, and that it grows in solutions containing sugar, decom- 

 posing the sugar by taking away certain of its chemical consti- 

 tuents required for its growth, and producing among other 

 products, alcohol, so these l)actcria, growing in animal and 

 vcgetal)le sul)stances, bring about by such growth their 

 decomposition, and were it not for this minute form of 

 vegetable life there would be no such thing as decomposi- 

 tion after death, except by the slow process of chemical 

 changes,' which would require ages to bring about the de- 

 struction of the bodies of even the smallest animals. 



You w^ill begin to ask, I presume, " What has all this to 

 do with contagious diseases and the protection of our liomes 

 from their ravages?" That I am about to try and tell you,. 



