l66 PREPARATION OF THE SUBSTRATES 



red colour of the blood indicates to us that it is still 

 present. If we use hydrogen peroxide, then we lose 

 any control over the blood contained in the tissue. 

 If one is not quite certain of the fact that the organ 

 is free from blood, one should squeeze out a few 

 pieces of it in a little water, and examine the fluid 

 with the spectroscope. 



About a hundred times more distilled water than 

 there is of the tissue is placed in an enamelled vessel 

 and then brought to the boil. The tissue, having 

 been absolutely freed from blood, is placed in the 

 boiling water, for every litre of which it is advisable 

 to add about five drops of glacial acetic acid. This 

 is boiled for ten minutes, and the boiling water is 

 passed through a sieve; the tissue is thoroughly 

 rinsed for about five minutes with distilled water, 

 and the same process of boiling is repeated, using 

 fresh water without the addition of acetic acid. The 

 boiling, the pouring off of the boiled water, the 

 rinsing of the tissues, and the renewed boiling are 

 repeated about six times without interruption. If it 

 is necessary to cease boiling, then one must never 

 forget to pour a fairly large quantity of toluol on the 

 top of the boiled water containing the tissue. If 

 this be omitted the tissue is liable to become infected, 

 and then some hours of boiling may be necessary in 

 order to free the organ again from extractive sub- 

 stances which react with ninhydrin. 



