266 THE FLOATING-MATTER OF THE AIR. 



one great advance made by modem science •was in the 

 direction of biology, or the science of life ; and that in 

 this new direction scientific inquiry, though at the 

 outset pursued at the cost of some temporary sufifering, 

 would in the end prove a thousand times more benefi- 

 cent than it had ever hitherto been . I said this because 

 I saw that the very researches which the lady deprecated 

 were leading us to such a knowledge of epidemic diseases 

 as will enable us finally to sweep these scourges of the 

 human race from the face of the earth. 



This is a point of such capital importance that I 

 should like to bring it home to your intelligence by a 

 single trustworthy illustration. In 1850, two distin- 

 guished French observers, MM. Davainne and Rayer, 

 noticed in the blood of animals which had died of the 

 virulent disease called splenic fever, small microscopic 

 organisms resembling transparent rods ; but neither of 

 them at that time attached any significance to the 

 observation. In 1861, Pasteur published a memoir on 

 the fermentation of butyric acid, wherein he described 

 the organism which provoked it ; and after reading this 

 memoir it occurred to Davainne that splenic fever might 

 be a case of fermentation set up within the animal body, 

 by the organisms which had been observed by him and 

 Eayer. This idea has been placed beyond all doubt by 

 subsequent research. 



Observations of the highest importance have also 

 been made on splenic fever by PoUender and BraueU. 

 Two years ago, Dr. Burden Sanderson gave us a very 

 clear account of what was known up to that time of 

 this disorder. With regard to the permanence of the 

 contagium, it had been proved to hang for years about 

 localities where it had once prevailed ; and this seemed 

 to show that the rod-like organisms could not con- 

 stitute the contagium, because their infective power 



