PREPARATIpN OF CULTURE MEDIA ; 



the culture medium, and differs in the case of different bac- 

 teria; the process of freeing* this soil from bacteria and their 

 spores is called sterilization, and we insure a suitable tempera- 

 ture by means of an incubator, the heat of which is kept 

 constant. 



The culture media which are used for special purposes are 

 almost innumerable, but in the daily routine of the laboratory 

 and for diagnostic purposes, broth, gelatin, agar-agar, and 

 blood-serum are all that are really necessary in the vast 

 majority of cases. These media may all be bought from any 

 firm of manufacturing- chemists, or from any bacteriological 

 laboratory; and their purchase saves a great deal of work, and 

 is to be recommended for those who only wish to use them 

 occasionally. They are sold in test-tubes, which are kept 

 sterile by being plugged fairly firmly with cotton-wool; this 

 substance prevents the passage of bacteria as long as it is kept 

 dry. The tubes are best stored in jars provided with tightly 

 fitting lids, and it is an advantage to place a shallow layer of 

 a solution of perchloride of mercury (or other non-volatile 

 antiseptic) in the bottom of each jar to prevent the medium 

 from drying up. It is scarcely necessary to add that not the 

 smallest trace of the lotion should be allowed to come into 

 contact with the cotton-wool plug- of the tubes. Or the 

 medium may be kept from drying up by covering the tubes 

 with indiarubber caps sold for the purpose. 



Messrs. Burroughs and Wellcome now manufacture certain 

 culture media in tabloid form. To prepare broth or agar-agar 

 it is only necessary to place a suitable tabloid in a sterilized 

 test-tube containing 5 c.c. of water. The tube is now plugged 

 with cotton-wool and boiled until the tabloid is completely 

 dissolved. This will be hastened if it is crushed or powdered 

 previously. If the water used is free from spores, as a rule 

 the culture medium is sterile, but where an autoclave is at 

 hand it should be used. These tabloids will be found very 

 convenient for practitioners who are not engaged in regular 

 bacteriological work. 



BROTH is very easily made, and, as it is the foundation of 

 many other media, the practitioner is strongly advised to pre- 

 pare it for himself. 



Requisites. i. Liebig's Extract of Meat. 



2. Peptone. 



