1870—1872 205 



that seemed necessary to their perfect growth, in a stove heated 

 to a temperature of 20° C. ; but in spite of every care, after 

 forty days had passed, the tiny fungus was languishing and 

 unhealthy. A temperature of 30° did not seem more successful ; 

 and when the stove was heated to above 38° the result was the 

 same. At 35°, with a moist and changing atmosphere, the re- 

 sult was favourable — very fortunately for Eaulin, for the 

 principal of the college, an economically minded man, did not 

 approve of burning so much gas for such a tiny fungus and with 

 such poor results. This want of sympathy excited Kaulin's 

 solemn wrath and caused him to meditate dark projects of 

 revenge, such as ignoring his enemy in the street on some future 

 occasion. In the meanwhile he continued his slow and careful 

 experiments. He succeeded at last in composing a liquid, tech- 

 nically called Eaulin's liquid, in which the aspergillus niger 

 grew and flourished within six or even three days. Eleven sub- 

 stances were necessary : water, candied sugar, tartaric acid, 

 nitrate of ammonia, phosphate of ammonia, carbonate of 

 potash, carbonate of magnesia, sulphate of ammonia, sulphate 

 of zinc, sulphate of iron, and silicate of potash. He now 

 studied the part played by each of those elements, varying his 

 quantities, taking away one substance and adding another, and 

 obtained some very curious results. For instance, the asper- 

 gillus was extraordinarily sensitive to the action of zinc ; if 

 the quantity of zinc was reduced by a few milligrams the vegeta- 

 tion decreased by one-tenth. Other elements were pernicious; 

 if Eaulin added to his liquid T ^&rnro of nitrate of silver, the 

 growth of the fungus ceased. Moreover, if he placed the liquid 

 in a silver goblet instead of a china saucer, the vegetation did 

 not even begin, " though," writes M. Duclaux, analysing this 

 fine work of his fellow student, "it is almost impossible to 

 chemically detect any dissolution of the silver into the liquid. 

 But the fungus proves it by dying." 



In this thesis, now a classic, which only appeared in 1870, 

 Eaulin enumerated with joyful gratitude all that he owed to his 

 illustrious master— general views, principles and methods, sug- 

 gestive ideas, advice and encouragement — saying that Pasteur 

 had shown him the road on which he had travelled so far. 

 Pasteur, touched by his pupil's affection, wrote to thank him, 

 saying : " You credit me with too much ; it is enough for me 

 that your work should be known as having been begun in my 



