16 BIOLOGY 



that the air was sterile, that is, pure, so far as any floating 

 particles were concerned, and that his box was ready for 

 experiment. 



At the bottom of the box were a series of tubes whose mouths 

 opened into the box but whose lower ends projected below; 

 Fig. 3 b. By means of the long tube, c, which could be 

 moved to and fro (since it passed through a rubber diaphragm, 

 d), all the test tubes could be filled successively with any of 

 the solutions with which he wished to experiment. In these 

 tests, Tyndall used various materials: old meat, old cheese, 

 hay infusion, etc., besides many other substances that pre- 

 vious experimenters had used in their attempt to settle the 

 question. After filling the tubes with these various materials, 

 they were heated to a temperature sufficiently high to destroy 

 all life that they might have contained in the beginning. This 

 was easily done, since the lower end of the tubes projected 

 below the level of the box and could be very easily put into 

 a bath of oil or brine, and heated to any desired temperature. 

 Any steam or vapor that might arise from the open end of 

 the test tube would pass into the box and readily find exit 

 through the glass tube at the top. Upon cooling, a fresh 

 supply of air would be drawn back into the box through the 

 curved tube a, but, as already indicated, no dust particles 

 would find entrance. Having thus, by heat, killed any living 

 organisms that might be in the solutions to be tested, he 

 again set the boxes aside and watched day by day to see 

 what would happen. Since everything was clearly visible to 

 the eye, it was possible to determine very quickly and surely 

 whether any living organisms developed in the test tubes. 



Tyndall's care in his experiments was so great that they were 

 quite beyond criticism. His experiments showed the cause of 

 previous errors and explained why there had been such con- 

 flict in the earlier experiments. He demonstrated among other 

 things that some forms of life, called spores, might remain 

 alive in boiling water for some time. This conclusion had been 



