476 



POPULAR SCIENCE MONTHLY. 



minutes later Petri dishes were prepared from each tube, with the fol- 

 lowing results: 



Antiseptic. 



5 per cent. Carbolic Acid 



95 per cent. Alcohol , 



Salicylic Acid (Sat. sol.) , 



xfc per cent. Mercuric Chloride | 3640 



2 c.c. 



20 

 1 



15 

 



10. To disinfect a Boom. — Three slips of filter paper were moist- 

 ened with a beef-broth culture of typhoid, and placed in large glass 

 jars. In the first jar sulphur was burned. Into the second jar forma- 

 line vapor was passed. The third jar was not treated with a disin- 

 fectant. A few hours later, Petri dishes were prepared from each 

 paper. They showed the following counts: 



No disinfectant 100,000 colonies. 



Sulphur fumes 6 " 



Formaline vapor " 



11. To show the Effect of Food Preservatives on the Pate of Mul- 

 tiplication 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: 



No preservative 7,520 colonies. 



Salt 850 



12. To shoiv the Antiseptic Properties of Gastric Juice. — An arti- 

 ficial gastric juice was prepared by dissolving a little pepsin in a ^ 

 per cent, solution of hydrochloric acid. To 1 c.c. of this juice, 14 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. 



minutes 35,200 colonies. 



2 " 157 



15 " 3 



30 " 



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 



