78 SOLID CULTIVATION MEDIA. 



to be charged with the nutrient jelly. The contents of one of the 

 sterile stock-flasks are liquefied by heating, and a glass pipette is 

 sterilised preparatory to transferring some of the stock jelly to the 

 test-tubes. The pipette is either superheated in the flame of a 

 Bunsen burner, or exposed to a temperature of lyo" C. in the dry air 

 steriliser for an hour, or it may be thoroughly washed, first with a 

 mercuric perchloride solution (aqueous i in looo), and then in 

 absolute alcohol, and dried. The sterile pipette is introduced into 

 one of the stock-flasks, and lo c.c. of the liquefied contents drawn 

 up into it by suction. The upper end of the pipette is then stoppered 

 by the finger to prevent its contents from' escaping, until they are 

 introduced into one of the sterile test-tubes. The sterile plug is 

 removed from one of these, and the liquefied jelly is allowed to 

 flow slowly to the bottom of the tube, care being taken that the liquid 

 do not touch the sides of the tube in its descent. The cotton 

 wool plug is then returned, and the tube, with its contents, is 

 placed upright, and allowed to cool. The lo c.c. of jelly which the 

 tube contains soon solidifies, and the tubes thus prepared, if they 

 show no reaction after the lapse of a week, may be assumed to be 

 sterile, and used as a cultivating soil for micro-organisms. If the 

 atmosphere is densely germ-laden (as during the summer and autumn 

 months), the transference of jelly from the stock-flasks to test-tubes 



should be effected under the carbolic spray, ^ or the test-tubes, when 



- 



' The question as to whether the carbolic spray is a reliable means of prevent- 

 ing contamination in cultivations in those manipulations which necessitate a free 

 access of the atmosphere to the sterile media, is one of great importance. During 

 certain periods of the year the atmosphere is so densely germ-laden as to render it 

 a matter of the greatest difficulty to prevent septic contamination. Our experience 

 proves that if an efficient spray be employed, this danger can be entirely avoided. 

 The spray used must produce a vapour in which carbolic acid is present at least 

 in the proportion of one part to thirty parts of water. A spray, cloud of this 

 strength is an efficient: antiseptic, and, applied under these conditions, the steam 

 spray is a weapon of precision that may be thoroughly depended on. And in 

 judging of the efficiency of an antiseptic for these purposes, a sufficient standard of 

 comparison is supplied by the ordinary spores usually present in the atmosphere ; 

 for if an antiseptic be powerful enough to destroy these, it should be considered 

 efficient, and its potency should not be judged by its ability or inability to destroy 

 certain rare and very resistant living structures, such as the spores of Bacillus 

 anthracis. A comparison based on the latter data is to some extent misleading, and 

 has tended to throw discredit on some antiseptics which' general experience has 

 proved to be useful and reliable. 



