454 BACTERIOLOGY. 



which this has been determined). Then transfer a drop 

 of the mixture to each of three liquefied agar-agar 

 tubes and pour them into Petri dishes. Place them 

 in the incubator and observe them for twenty-four, 

 forty-eight, and seventy-two hours. No growth occurs. 

 How is this to be accounted for ? 



At the end of seventy-two hours inoculate all of 

 these plates with a culture of the same organism which 

 has not been exposed to sublimate, by taking up bits of 

 the culture on the needle and drawing it across the 

 plates. A growth now results. We have here an ex- 

 periment in which organisms which have been exposed 

 to sublimate for a much shorter time than necessary to 

 destroy them, when transferred directly to a favorable 

 culture medium do not grow, and yet, when the same 

 organism which has not been exposed to sublimate is 

 planted upon the same medium it does grow. How is 

 this to be accounted for ? 



Skin-disinfection. — With a sterilized knife scrape 

 from the skin of the hands, at the root of the nails and 

 under the nails, small particles of epidermis. Prepare 

 plates from them. Note the results. 



Wash the hands carefully for ten minutes in hot 

 water and scrub them during this time with soap and a 

 sterilized brush. Rinse them in hot water. Again 

 prepare plates from scrapings of the skin on the fingers, 

 at the root of the nails, and under the nails. Note the 

 results. 



Again, wash as before in hot water with soap and 

 brush, rinse in, hot water, then soak the hands for five 

 minutes in 1 : 1000 corrosive sublimate solution, and, as 

 before, prepare plates from scrapings from the same 

 localities. Note the results. 



