544 Preston Kyes, 



logical evidence as to this function on the part of certain endo- 

 thelial cells. 



When bacteria or other minute foreign bodies are injected 

 into the circulating blood stream of pigeons, they are rapidly- 

 withdrawn from the circulation into the tissues of the liver and 

 spleen. Examination of these tissues shows also, that the foreign 

 bodies are there contained within cells of a distinct type, which type 

 is the same for both the liver and the spleen. This type of cell 

 moreover, contains in addition to the foreign substances injected, much 

 golden yellow pigment, and when tested for iron by Perl's method 

 this included pigment gives a positive Prussian-blue reaction of such 

 intensity that the containing cell is clearly differentiated from sur- 

 rounding tissue components. When combined therefore, with suitable 

 counterstains, the iron reaction affords a favorable histological method 

 for the study of such cells. The method moreover, is applicable to 

 the study of the same cells in normal tissues, for its use shows that 

 this pigment content is not incidental to experimental or pathological 

 changes but is constantly present under normal conditions. In detail 

 the procedure which has been employed in the study of the tissues 

 of eigtheen normal pigeons here discussed, is as follows: 



Fix thin slices of tissue for 18—24 hours in Miiller's fluid plus 5 per cent 

 mercuric sublimate. Imbed in paraffin and section to 4 microns. Fix sections to 

 slide and stain 20 — 40 minutes with acid carmine. Wash, and transfer to equal 

 parts of a 2 per cent aqueous solution of potassium ferrocyanide and of a 2 per 

 cent, aqueous solution of hydrochloric acid. Remove after from 3 to 10 minutes, 

 wash in distilled water and pass quickly through a 0,5 percent aqueous erythrosin 

 solution. Dehydrate in alcohol, clear in xylol and mount in Canada balsam. 



Specimens of normal liver and spleen prepared according to the 

 above method, display in contrast to other tissues of the pigeon, an 

 extensive content of cells possessing the distinct blue tone of the 

 Prussian-blue iron reaction. These cells are distributed rather evenly 

 throughout both organs but more numerously in the liver. Under low 

 powers of the microscope their general morphology indicates that the 

 iron-contaning cells are of the same type in the two organs, and as 

 will be seen later, this is supported by a correspondence in their 

 finer structure and physiology. In as much as the relation of these 



