THE ART OF SCIENTIFIC INVESTIGATION 



solution. Gram found that after this treatment the tissue was 

 rapidly decolourised by alcohol but that certain bacteria remained 

 blue-black. The gentian violet and iodine had unexpectedly 

 reacted with each other and with a substance present in some 

 bacteria and not others, thus providing not only a good stain but 

 also a simple test which has proved of the greatest value in 

 distinguishing different bacteria. ^°^ 



While engaged in studying the function of the pancreas in 

 digestion in 1889 at Strasbourg, Professors von Mering and 

 Minkowski removed that organ from a dog by operation. Later 

 a laboratory assistant noticed that swarms of flies were attracted 

 by the urine of the operated dog. He brought this to the attention 

 of Minkowski, who analysed the urine and found sugar in it. 

 It was this finding that led to our understanding of diabetes and 

 its subsequent control by insulin. ^^ More recently the Scotsman, 

 Shaw Dunn, was investigating the cause of the kidney damage 

 which follows a severe crush injury to a limb. Among other 

 things he injected alloxan and he found that it caused necrosis 

 of the islet tissue of the pancreas. This unexpected finding has 

 provided a most useful tool in the study of diabetes.^^ 



The French physiologist, Charles Richet, was testing an extract 

 of the tentacles of a sea anemone on laboratory animals to 

 determine the toxic dose when he found that a small second dose 

 given some time after the first was often promptly fatal. He 

 was at first so astounded at this result that he could hardly believe 

 that it was due to anything he had done. Indeed he said it was 

 in spite of himself that he discovered induced sensitisation or 

 anaphylaxis and that he would never have believed that it was 

 possible." Another manifestation of the same phenomenon was 

 discovered independently by Sir Henry Dale. He was applying 

 serum to strips of involuntary muscle taken from guinea-pigs 

 when he encountered one that reacted violently to the application 

 of horse serum. Seeking an explanation of this extraordinary 

 observation he found that that guinea-pig had some time 

 previously been injected with horse serum. ^^ 



It was the usual practice among physiologists to use physio- 

 logical saline as a perfusion fluid during experiments on isolated 

 frogs' hearts. By this means they could be kept beating for 

 perhaps half an hour. Once at the London University College 



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