TANGIBLE CAUSES OF DISEASE 241 



make its next great advance, is the assistance of 

 a great chemist, such as he who presided at its 

 birth. 



Robert Koch to whom bacteriology owes many 

 of its successful experimental methods formulated 

 certain postulates which must be fulfilled before a 

 particular organism can be held to be responsible 

 for a given disease. It must be identified in the 

 diseased tissues, cultivated outside the body, 

 reproduce the same disease in animals, and again 

 be found multiplying in the tissues of these animals. 

 In connection with the great majority of infective 

 and contagious diseases these criteria are now 

 fulfilled, and we know the specific agent in each 

 case. Consider how much this means. Before 

 Pasteur, the physician, when face to face with a 

 case of fever, had to act in complete ignorance of 

 any tangible reason for the symptoms he beheld. 

 If he thought about causation at all, little more 

 than words and phrases were available for the 

 assistance of his thought. Now he can actually 

 handle the 'cause' of each fever. It is a living 

 thing, having qualities and habits with which he 

 can become intimate. As a consequence the whole 

 attitude of the doctor's mind is altered. Diagnosis 

 may be a matter of certainty ; treatment has entered 

 upon an entirely new era. 



Since Pasteur, we have gradually come to 

 recognise how great a part the lowest and most 

 minute of living organisms play in the economy 



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