PREPARATION OF THE SUBSTRATES 167 



If a centrifuge be at one's disposal, the boiling 

 water is centrifuged at a suitable speed. This is 

 still more necessary when one is working with finely 

 minced organs or bacteriological cultures and the 

 like, otherwise too much of the material would be 

 lost when pouring off the water. 



After the sixth boiling only five times the amount 

 of water at most is used. The smaller the amount of 

 water employed, the more exact is the result of the test 

 for the extractive substances that react with ninhydrin. 

 In every case as much water must be present as will 

 be needed to continue active boiling for five minutes 

 without the risk of burning, the smallest possible 

 vessels being used. Then a certain quantity of 

 boiled water is filtered through a hardened filter paper. 

 To 5 c.c. of the filtrate is added at least i c.c. of a 

 i per cent, aqueous solution of ninhydrin, and the 

 mixture is boiled (as described on p. 160 seq.) for one 

 minute. If, after half an hour, not the slightest trace 

 of a violet coloration manifests itself, the organ may 

 be considered as suitable, provfded it still remains 

 snow-white. Only the tissues of the liver, the spleen, 

 and the kidneys do not appear quite white. Should 

 the tissue turn grey, or even brown, during boiling, 

 this is a proof that it was not absolutely freed from 

 blood, or that the boiling was not conducted properly. 

 Should the particular test prove positive, the boiling 

 must be continued i.e., the water must be poured 



