was placed in a sterile glass vessel and allowed to clot. After standing some time, serum separated. One cubic centimeter of this serum was placed in a small test-tube and five loops full of a beef-broth culture of typhoid bacilli were added to it. Petri dishes were made from this mixture at intervals for an hour. To get an idea of the number of germs originally placed in the serum, a control was run with 1 c.c. of sterile water. The count made from this control is recorded as the count for 0minutes.
| 0 | minutes | 3,760 | colonies. | |
| 2 | " | 737 | " | |
| 8 | " | 810 | " | |
| 15 | " | 34 | " | |
| 30 | " | 2 | " | |
| 60 | " | 0 | " |
12. To show that Bacteria are not given off from a Moist Surface.—A culture of harmless, brilliant yellow bacteria was smeared on the inside of a large glass tube. Through this tube a strong current of air was directed on to agar in a Petri dish. If bacteria were given off into the air from the moist surface, they would be blown upon the agar, where they would develop into colonies. The Petri dish used in this experiment developed no yellow colonies. The smear was now allowed to dry and was then crushed with a sterile glass rod. A second current of air was now directed through the tube into another Petri dish. This dish developed 240 colonies of yellow bacteria.
The above is merely suggestive of the kind of work that might be done in any secondary school. Most of these experiments could be performed by the average high school senior. All of them could be used as class demonstrations. Each one has a direct bearing on some large question of preventive medicine. A week's training in bacteriological technic will enable any teacher to give this work.
The experiments here outlined were suggested to me by Dr. W. H. Manwaring, and were carried out in the Pathological Laboratory of the University of Chicago, during the summer of 1904.
