xii INTRODUCTION. 



devoted and admiring son-in-law, M. Valery Kadot. It 

 is the record of a life of extraordinary scientific ardour 

 and success, the picture of a mind on which facts fall 

 like germs upon a nutritive soil, and, like germs so 

 favoured, undergo rapid increase and multiplication. 

 One hardly knows which to admire most the in- 

 tuitive vision which discerns in advance the new 

 issues to which existing data point, or the skill in 

 device, the adaptation of means to ends, whereby the 

 intuition is broughf to the test and ordeal of experi- 

 ment. 



In the investigation of microscopic organisms the 

 ' infinitely little,' as Pouchet loved to call them and 

 their doings in this our world, M. Pasteur has found 

 his true vocation. In this broad field it has been his 

 good fortune to alight upon a crowd of connected 

 problems of the highest public and scientific interest, 

 ripe for solution, and requiring for their successful 

 treatment the precise culture and capacities which he 

 has brought to bear upon them. He may regret his 

 abandonment of molecular physics; he may look 

 fondly back upon the hopes with which his researches 

 on the tartrates and paratartrates inspired him ; he 

 may think that great things awaited him had he 

 continued to labour in this line. I do not doubt it. 

 But this does not shake my conviction that he yielded 

 to the natural affinities of his intt-lU ct, that he obeyed 

 its truest impulses, and reaped its richest rewards, in 



