APPENDIX 



cyanide left on the bench near his vacuum tube became fluores- 

 cent ahhough separated from the tube by black paper. He 

 afterwards said : " I found by accident that the rays penetrated 

 black paper."* 



(4) When W. H. Perkin was only eighteen years old he tried 

 to produce quinine by the oxidation of allyl-o-toluidine by 

 potassium dichromate. He failed, but thought it might be 

 interesting to see what happened when a simpler base was 

 treated with the same oxidiser. He chose aniline sulphate and 

 thus produced the first aniline dye. But chance played an even 

 bigger part than the bare facts indicate : had not his aniline 

 contained as an impurity some p-toluidine the reaction could 

 not have occurred.* 



(5) During the first half of the nineteenth century it was 

 firmly believed that animals were unable to manufacture carbo- 

 hydrates, fats or proteins, all of which had to be obtained in 

 the diet preformed from plants. All organic compounds were 

 believed to be synthesised in plants whereas animals were thought 

 to be capable only of breaking them down. Claude Bernard 

 set out to investigate the metabolism of sugar and in particular 

 to find where it is broken down. He fed a dog a diet rich in 

 sugar and then examined the blood leaving the liver to see if 

 the sugar had been broken down in the liver. He found a 

 high sugar content, and then wisely carried out a similar 

 estimation with a dog fed a sugar-free meal. To his astonish- 

 ment he found also a high sugar content in the control animal's 

 hepatic blood. He realised that contrary to all prevailing views 

 the liver probably did produce sugar from something which is 

 not sugar. Thereupon he set about an exhaustive series of 

 experiments which firmly established the glycogenic activity of 

 the liver. This discovery was due firstly to the fact that Bernard 

 was meticulous in controlling every stage of his experiments, and 

 secondly, to his ability to recognise the importance of a result 

 discordant with prevailing ideas on the subject and to follow 

 up the clue thus given.^^ 



(6) A mixture of lime and copper sulphate was sprayed on 

 posts supporting grape vines in Medoc with the object of 

 frightening away pilferers. Millardet later noticed that leaves 

 accidentally sprayed with the mixture were free from mildew. 



161 



