xiv INTRODUCTION 



has a great .man been able to pay such a tribute to his father 

 as that paid by Pasteur : " For thirty years I have been his 

 constant care, I owe everything to him." 



This is a biography for young men of science, and for others 

 who wish to learn what science has done, and may do, for 

 humanity. From it may be gleaned three lessons. 



The value of method, of technique, in the hands of a great 

 master has never been better illustrated. Just as Harvey, 

 searching out Nature by way of experiment, opened the way 

 for a study of the functions of the body in health, so did 

 Pasteur, bringing to the problems of biology the same great 

 organon, shed a light upon processes the nature of which had 

 defied the analysis of the keenest minds. From Dumas's 

 letter to Pasteur, quoted in Chapter VI., a paragraph may 

 be given in illustration : " The art of observation and that of 

 experiment are very distinct. In the first case, the fact may 

 either proceed from logical reasons or be mere good fortune; 

 it is sufficient to have some penetration and the sense of truth 

 in order to profit by it. But the art of experimentation 

 leads from the first to the last link of the chain, without 

 hesitation and without a blank, making successive use of 

 Reason, which suggests an alternative, and of Experience, 

 which decides on it, until, starting from a faint glimmer, the 

 full blaze of light is reached." Pasteur had the good fortune 

 to begin with chemistry, and with the science of crystallo- 

 graphy, which demanded extraordinary accuracy, and developed 

 that patient persistence so characteristic of all his researches. 



In the life of a young man the most essential thing for 

 happiness is the gift of friendship. And here is the second 

 great lesson. As a Frenchman, Pasteur had the devotion that 

 marks the students of that nation to their masters, living and 

 dead. Not the least interesting parts of this work are the 

 glimpses we get of the great teachers with whom he came 

 in contact. What a model of a scientific man is shown in the 

 character of Biot, so keenly alive to the interests of his young 

 friend, whose brilliant career he followed with the devotion of 

 a second father. One of the most touching incidents recorded 



