PREFACE. 



IN the salon of a distinguished man, or of a great 

 writer, there is often to be found a person who, without 

 being either a fellow-worker or a disciple, without 

 even possessing the scientific or literary qualities which 

 might explain his habitual presence, lives nevertheless 

 in complete familiarity with the man whom all around 

 him call ' dear master.' Whence comes this intimate 

 one ? who is he ? what is his business ? He is only 

 known as a friend of the house. He has no other 

 title, and he is almost proud of having no other. 

 Stripped of his own personality, he speaks only of the 

 labours and the success of his illustrious friend, in 

 the radiance of whose glory he moves with delight. 



The author of this work is a person of this descrip- 

 tion. Intimately connected with the life of M. Pasteur, 

 and a constant inmate of his laboratory, he has passed 

 happy years near this great investigator, who has dis- 

 covered a new world the world of the infinitely little. 

 Since the first studies of M. Pasteur on molecular 



