204 THE LIFE OF PASTEUR 



vincial life to disturb you. Teach your pupils to the very best 

 of your ability and give up your leisure to experiments; this 

 was M. Biot's advice to myself." "When in July, 1863, he 

 began to fear that Raulin might allow imagination to lead him 

 astray in his work, he repeatedly advised him to state 

 nothing that could not be proved: *'Be very strict in 

 your deductions"; then, apparently, loth to damp the young 

 man's ardour: *'I have the greatest confidence in your judg- 

 ment; do not take too much heed of my observations." 



In 1863 Pasteur asked Raulin to come with him, Gernez and 

 Duclaux, to Arbois for some studies on wdnes, etc., but Raulin, 

 absorbed in the investigations he had undertaken, refused; in 

 1865 he refused to come to Alais, still being completely wrapt 

 up in the same work. Pasteur sympathized heartily with his 

 pupil's perseverance, and, when Raulin was at last able to 

 announce to his master the results so long sought after, Pasteur 

 hurried to Caen, where Raulin was now professor of Physics, 

 and returned full of enthusiasm. His modesty in all that con- 

 cerned himself now giving way to delighted pride, he spoke of 

 Raulin 's discoveries to every one. Yet they concerned an 

 apparently unimportant subject — a microscopical fungus, a 

 simple mucor, whose spores, mingled with atmospheric germs, 

 develop on bread moistened with vinegar or on a slice of lemon ; 

 yet no precious plant ever inspired more care or solicitude than 

 that aspergillus niger, as it is called. Raulin, inspired by 

 Pasteur's studies on cultures in an artificial medium, that is, a 

 medium exclusively composed of defined chemical substances, 

 resolved to find for this plant a typical medium capable of giving 

 its maximum development to the aspergillus niger. Some of 

 his comrades looked upon this as upon a sort of laboratory 

 amusement; but Raulin, ever a man of one idea, looked upon 

 the culture of miscroscopic vegetation as a step towards a greater 

 knowledge of vegetable physiology, leading to the development 

 of artificial manure production, and from that to the rational 

 nu rition of the human organisms. He started from the condi- 

 tions indicated by Pasteur for the development of mucedinas in 

 general and in particular for a mucor which has some points of 

 resemblance with the aspergillus niger, the penicUlium glau- 

 cum, which spreads a bluish tint over mouldy bread, jam, and 

 soft cheeses. Raulin began by placing pure spores of asper- 

 gillus niger on the surface of a saucer comtaining everything 



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