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IV. — On the Cultivation of Bacteria. 

 By Edgar M. Crookshank, M.B. Lond., F.R.M.S. 



QRead 9th December, 1885.) 



Plates III.-V. 



In the course of my remarks this evening upon the cultivation of 

 bacteria, I shall touch upon several points which are well known 

 to the Society. They will, however, lead me to bring forward 

 many facts of extreme interest, and I trust of importance also, in 

 that they disclose fresh fields for micro-biological research. 



As is well known, there has been given during the last few 

 years, more especially on the Continent, a very wide-spread 

 stimulus to the study of bacteria. This is due in great measure 

 to the encouraging results which have been obtained by employ- 

 ing the improved methods recently introduced for investigating 

 micro-organisms. 



The methods of cultivation on solid media have in many 

 laboratories taken the place, almost entirely, of the old methods in 

 which nutrient liquids were employed. I shall draw attention 

 to some of the advantages offered by solid media, which may 

 explain the reason for this change. 



In the first place, the most essential thing in order to study 

 the life-history of a particular micro-organism is to obtain and to 

 maintain a "pure-cultivation." In the case of the pathogenic 

 bacteria, this is emphasized by Koch as follows. Koch maintains 

 that to prove satisfactorily that a particular micro-organism 

 is the cause of a disease — 



Firstly. — The micro-organism must be found in the blood, 

 lymph, or diseased tissues, of man or animal suflfering from, or 

 dead of the disease. 



Secondhj. — The micro-organism must be isolated from the 

 blood, lymph, or tissues, and cultivated in suitable media. These 

 'pure cultivations must be carried on through successive genera- 

 tions of the micro-organism. 



Thirdly. — A pure cultivation thus obtained must, when 

 introduced into the body of a healthy animal, produce the disease 

 in question. 



Lastly. — In the inoculated animal the same micro-organism 

 must again be found. 



Now, in the case of liquid nutrient media, it was no easy 

 matter to obtain and maintain a pure cultivation. 



If a drop of liquid containing several kinds of bacteria be 

 introduced into a nutrient liquid, we have a mixed cultivation from 



