CONTAGIOUS DISEASES. 261 



clothing and iuruiturc. Now, let us take a little of this 

 mould and place it under the microscope, when we shall see 

 what is pictured here on the screen. (Picture of one of the 

 common forms of mould shown.) This mould, like every 

 other form of vegetable life, grows from a germ or seed, 

 and to grow and develop so extensively in our houses and 

 elsewhere as we know it does, under proper conditions of 

 moisture and warmth, the germs or seed must first be sown. 

 Now, let us see if we can learn, by investigation, how these 

 germs of this little plant are so universally distributed. 



As this plant, like all others, requires some form of mat- 

 ter to feed and grow upon, we will select for our experiment 

 a small piece of blackened leather, as everyone knows how 

 readily mould grows upon this material, — in fact, we can 

 hardly keep our shoes from becoming mouldy in damp, sum- 

 mer weather, if they arc put away for a day or two, — we 

 will take three small glass tubes, such as you see repre- 

 sented on the screen (illustration shown) , into each one we 

 will put a little water and also a small piece of the leather, 

 fixing the latter so that it will rest just above or on the 

 surface of the water. Into the mouths of two of the tubes 

 we will put plugs of cotton wool. Then we will place these 

 three tubes, with their contents, in an oven and heat them 

 until the temperature is at or near the boiling point. This 

 will destroy any kind of germ life that may bo in the water 

 or air in the tubes. Then we will put these tubes away in a 

 warm, damp place. In three or four days we examine them, 

 Avhen we find the piece of leather in the tube without the 

 cotton plug covered with a fine mould or mildew, while the 

 pieces of leather in the other tubes remain unchanged. We 

 will put them away for a few days more and then examine 

 them again, when we find a vigorous growth of mould in the 

 open tube, but none in the tubes with the cotton plugs. 

 Now, these tubes were all prepared alike, and they have 

 been under the same influence of warmth, moisture and air, 

 — for the air passes into the tubes through the meshes of the 

 cotton almost as readily as it would if they were removed, — 

 still, there has been no growth in the tubes with the cotton 

 plugs. Now, we will remove the plug of cotton from one of 

 these tubes, and allow it to remain open for an hour or two, 



