9 



very existence. The subject to which I refer is the part played 

 by certain micro-organisms in the economy of nature. 



The question covers such an extent of ground that I should 

 have prefeiTed to have plunged at once in medias res, but I must 

 ask the ibrgiveness of the more learned among my audience if I 

 begin at the beginning, for otherwise I fear that I should be 

 unable to make myself intelligible to those who have not paid 

 any special attention to the subject. 



An animal stricken, say with splenic fever, falls dead upon 

 the plain. In a short time certain alterations will be observed in 

 its condition. The tissues will soften, and give off offensive odours ; 

 in other words, will rot. At the same time the carcass will be 

 attacked by nature's scavengers in various forms — mammalia, birds, 

 insects, &c., and ultimately nothing but its bleaching bones will be 

 left to tell the tale. Now these changes have been brought about 

 by a series of causes which gi-aduate from the most obvious to the 

 most obscure. The coarser and more evident phenomena have 

 been known to men without doubt from time immemorial. When 

 Hamlet is asked as to the whereabouts of Polonius he replies " at 

 supper. Not where he eats, but where he is eaten — a certain con- 

 vocation of politic worms are e'en at him ... If you find him 

 not out within the month you shall nose him as you go up stairs 

 into the lobby." But they knew more than this. They knew that 

 these changes were influenced by conditions of heat, cold, moisture, 

 and dryness. Savage tribes have long used the heat of the sun 

 for drying and preserving flesh. They knew also that the contact 

 of a substance in a state of decomposition greatly accelerates 

 a similar change in another previously unaltered. The use of 

 leaven in bread making is an instance of this. Whether they 

 troubled tlieraselves to think about, or inquire into, the causes of 

 these phenomena, is quite another matter. If they did they were, 

 n) doubt, content to adopt the views of Dr. Watts with regard 

 to the combative propensities of the genus Canis that '• 'tis their 

 nature to." 



With the advance of Science naturally came an increased 

 desire for more knowledge of these and similar matters. The 

 chemists came first on the scene. They explained that the vital 

 force having been removed, the animal tissues were left a prey to 

 the ordinary physical forces, and that the complex organic com- 



