2 BACTERIOLOGY. 



coveries is evidenced by the fact that in Germany 

 medical men were summoned from all parts of 

 the country to Berlin to attend a course of 

 instruction in the latest methods employed in the 

 investigation of bacteria. In this way the methods 

 of pure cultivation devised by Koch, and the means 

 of recognising the cholera bacillus, are being widely 

 disseminated. 



To a medical man, those bacteria which are con- 

 nected with disease, and more especially those which 

 have been proved to be the causa, if not the actual 

 materies morbi, are of predominant interest and im- 

 portance. It is, however, impossible by localising 

 one's knowledge to pathogenic species to thoroughly 

 understand the life-history of these particular 

 forms, or to be able to grasp and appreciate 

 the various arguments and questions that arise 

 in comparing their life-history with the progress 

 of disease. 



It is not sufficient to know only how to 

 recognise and artificially cultivate a bacterium 

 associated with disease ; we must endeavour to 

 establish the exact relationship of the bacterium 

 to the disease in question. To ascertain beyond 

 all doubt whether a micro-organism is actually 

 the causa causans of a disease, Koch has laid 

 down the following postulates : 



a. The micro-organism must be found in the 

 blood, lymph, or diseased tissues of man, or animal, 

 suffering from, or dead of, the disease. 



