52 LABORATORY EXERCISES IN BACTERIOLOGY. 



mercuric chloride. After five minutes one of the threads is withdrawn 

 with a sterile (flamed) forceps, and divided into equal lengths by means 

 of a sterilized scissors. One of the latter bits is at once transferred to 

 a fresh tube of sterile nutrient substance. The second is gently washed 

 in sterile water to free it from the excess of the sublimate solution; then 

 washed for half a minute in a weak (two per cent.) solution of ammonium 

 sulphide in order to remove any possible coat of mercurial albuminate 

 from about the microorganisms and their spores. This is then rinsed off 

 by second immersion of the thread in sterile water, after which the thread 

 is transferred to a tube of sterile nutrient medium. The same procedures 

 are performed with the remaining bits of thread at the close of ten minutes, 

 twenty minutes, and thirty minutes. Each tube, properly marked, is 

 then placed in the incubator and observations made at the close of the 

 first, second, and third days. 



Exercise 19. Practise one of the methods of surgical disinfection of 

 the hands, inoculating sterile bouillon with scrapings from the hands and 

 material beneath the nails before the process as controls, and similarly 

 planting scrapings from the same sources after each stage of the pro- 

 cedure in order to determine the value of the several steps of the process. 

 In this exercise let the class be arranged in groups of five, each individual 

 planting the preliminary control tubes from the hand and nails. In 

 each group let one man carry out the process in full before making the 

 second inoculation. Let the second wash the hands with soap and hot 

 water, using a sterile hand brush for effectiveness; when, having rinsed 

 the hands in sterile water, let him make inoculations from the epiderm 

 and nails into sterile bouillon. The third should soak his hands for five 

 minutes in a i : 1000 solution of bichloride of mercury, working the dis- 

 infectant well into the skin by means of a sterilized hand brush; 

 after which, having rinsed his hands free from the disinfectant in 

 sterile water, let him make similar inoculations from the epiderm and 

 nail scrapings into sterile bouillon. A fourth should soak his hands in 

 a saturated solution of potassium permanganate, rinse off the excess in 

 sterile water, and make similar inoculations. The fifth should soak his 

 hands in a solution (saturated) of oxalic acid, rinse the hands in sterile 

 water, and likewise inoculate tubes of sterile bouillon with scrapings from 

 the skin surface and from the nails. Further, the third man of each 

 group, who has sterilized his hands with the sublimate solution alone, 

 should now soak his hands in a two per cent, solution of ammonium sul- 

 phide, brushing it well in, and again rinse off the chemical and make 

 inoculations from the same sources as before. Moreover, the first man, 

 who has carried out the entire process of hand sterilization, should make 



