30 MANUAL OF HISTOLOGY. 



METHODS OF INJECTING THE BLOOD-VESSELS. 1 



Good injections are hard to make, requiring skill, patience, 

 and practice. First of all, it is essential to have a perfectly 

 transparent injecting material. This is usually made up with 

 gelatine and colored by carmine or Prussian blue. When 

 carmine is used it is customary to dissolve it in ammonia, fil- 

 ter, and then add it to the solution of gelatine. In order to 

 obtain a neutral or faintly acid liquid, acetic acid is added, 

 drop by drop, until the alkalinity is overcome, but there must, 

 at the same time, be no precipitation of carmine, which is best 

 detected by the granules of carmine seen in the field of the 

 microscope. If alkaline, the color diffuses and the result is 

 a failure. 



It is difficult to lay down any rule in reference to the amount 

 of acetic acid necessary ; the color of the liquid is the best 

 and only satisfactory test. The ammoniacal odor, if very 

 slight, cannot be detected, and therefore is useless as a test. 

 A slight excess of acid, however, will do no harm. 



The preparation of the blue injecting fluid is less difficult. 



Usually Brucke's soluble Berlin blue is used; it can be 

 procured at most of the large drug stores, but if not obtaina- 

 ble, may be made as follows (Klein) : 



" Take of potassic ferrocyanide 217 grammes, and dissolve in 

 one litre of water (solution A). Take one litre of a ten per cent, 

 solution of ferric chloride (solution B). Take four litres of a 

 saturated solution of sulphate of soda (solution C). Add to 

 A and B two litres of C. Then, with constant stirring, pour 

 the ferric chloride mixture into a vessel, collect the precipitate 

 upon a flannel strainer, returning any blue fluid which at first 

 escapes through the pores of the flannel ; allow the solutions 

 to drain off. Pour a little distilled water over the blue mass, 

 returning the first washing if colored, and renew the water 

 from day to day until it drips through permanently of a deep 

 blue color. This is a sign that the salts are washed away, and 

 all that is further necessary is to collect the pasty mass from 

 the strainer and allow it to dry." 



Having obtained the soluble Berlin blue, it will be much 



1 Prepared for the editor by Dr. W. H. Porter, Curator of the Presbyterian Hos- 

 pital, New York city. 



