Page:Popular Science Monthly Volume 66.djvu/480

480 minutes later Petri dishes were prepared from each tube, with the following results:

10. To disinfect a Room.—Three slips of filter paper were moistened with a beef-broth culture of typhoid, and placed in large glass jars. In the first jar sulphur was burned. Into the second jar formaline vapor was passed. The third jar was not treated with a disinfectant. A few hours later, Petri dishes were prepared from each paper. They showed the following counts:

11. To show the Effect of Food Preservatives on the Pate of Multiplication of Bacteria.—Two test-tubes, each containing 5 c.c. of fresh milk, were used. A Petri dish made from the milk at this time showed 83 colonies of bacteria. To one of the tubes about two grams of common salt were added. The second tube was not treated. The tubes were kept in a locker over night. Petri dishes were then made from them with the following results:

12. To show the Antiseptic Properties of Gastric Juice.—An artificial gastric juice was prepared by dissolving a little pepsin in a per cent, solution of hydrochloric acid. To 1 c.c. of this juice, c.c. of a beef-broth culture of typhoid bacilli was added, and Petri dishes made from the mixture at intervals for half an hour. The number of colonies developing on these dishes is tabulated below. To get an idea of the number of germs originally added to the gastric juice, the same amount of typhoid culture was added to 1 c.c. of sterile water and a Petri dish prepared from this mixture. The number of colonies on this dish is recorded as the count for minutes.

13. To show the Antiseptic Properties of Human Serum.—Under the supervision of a physician, a small amount of blood was drawn, by means of a hypodermic needle, from a vein in the arm. This blood