6 CHOICE OF METHODS 



5. To Mark Selected Individual Cells or Tissues in Vivo 



FOR Later Examination 



In this connection we at once think of the vital stains, trypan blue, carmine, 

 India ink (carbon) and hundreds of others, which, when injected into the body, 

 are phagocytosed by the reticulo-endothelial cells (or macrophages). Pieces of 

 tissue can then be excised and the accumulations of stains can be studied within 

 the still living cells, that is supravitally, for unless cultured the cells are slowly 

 djdng. But, if desired, the tissues can be fixed and the results observed at 

 leisure in sections. 



It has long been known that bone laid down in the presence of Madder fed to 

 the animals is marked by the madder and can thus be distinguished from bone 

 deposited beforehand and afterwards. In the same way dentine can be marked 

 in vivo with Alizarin Red S. 



Another example of in vivo marking is the deposition of Prussian Blue. Thus 

 a slightly hypertonic solution (potassium ferrocyanide 0.5 gm., iron ammonium 

 citrate, 0.5 gm. and aq. dest. 50 cc.) injected into the subarachnoid space of the 

 spinal cord is useful in the localization of the pathways of drainage of cerebro- 

 spinal fluid, because of the marking secured when the tissues are fixed in 40% 

 formalin plus 1% concentrated hydrochloric acid by the deposition of Prussian 

 blue (Weed, L. H., J. Med. Res., 1914, 26, 21-117). 



The tissues of animals recently killed or under anesthesia can be selectively 

 marked with various dyes by Perfusion of the blood vessels with dilute solutions 

 of dyes. The outstanding methods in this group have been devised by Bensley 

 (R. R., Am. J. Anat., 1911, 12, 297-388) for histological analysis of the epithelial 

 components of the pancreas and stomach. Dilute solutions of the dyes in physio- 

 logical saline are injected into the thoracic aorta of an animal killed by bleeding. 

 Pieces of pancreas and gastric mucous membrane are then removed and examined 

 fresh. Neutral red picks out the Islets of Langerhans of the pancreas, pyronin 

 the duct system of the pancreas, naphthol blue the parietal cells of the Stomach 

 and so on. In the same way Nerve Fibers can be marked for subsequent study 

 by vascular perfusion with methylene blue and degenerating nerve fibers in 

 poliomyelitis (and presumably in other conditions) can be sharply differentiated 

 from uninjured ones by the fact that they take up neutral red (Covell, W. P. 

 and O'Leary, J. L., Arch. Neurol. & Psych., 1932, 27, 518-524). It has long 

 been known that the best way to mark renal glomeruli is to perfuse in the same 

 fashion with a dilute solution of janus blue. The glomeruli stand out clearly in 

 the fresh kidney by their deep blue color in a red background (Cowdry, E. V., 

 Contrib. to Embryol., Carnegie Institution of Washington, 1918, No. 25, 39- 

 160). A similar selective staining in less brilliant colors is obtainable wrlh. janus 

 green. Relatively permanent preparations can be made of some of these 

 specimens. 



The same dyes, and many others, can also be applied in dilute solutions to 

 cells freshly removed from the body and which are still living. Such methods 



