32 FRANK ADAM McJUNKIN 
the ingestion of microscopic particles as well as to the ‘drinking 
in’ of colloids (ultramicroscopic). In a small series of rabbits 
injected with trypan blue and with a carmine solution used by 
Kiyono (’13) practically the same results have been obtained by 
the writer. The probable explanation of the absence of vitally 
stained cells in the peripheral blood is given below. Conflicting 
opinions have arisen about the specificity of the cells stained by 
this method rather than in regard to the presence of the dye in 
the endothelial lining of blood-vessels. Evans (’15) speaks of 
macrophages other than the vascular ones which are more or 
less fixed and probably of endothelial origin. This view of 
tissue spaces lined with endothelium is scarcely in accord with 
most work which shows that not only the blood-vessels, but the 
lymph-vessels as well are closed endothelial lined. tubes (Mac- 
Callum, ’03). y 
In the first experiments with lampblack it was found that 
this substance is removed from lampblack-citrate suspensions by 
filtration through muslin, but that it passes through if blood is 
added to the suspension before filtration. This corresponds in 
general to what is known as protective colloid action, and later 
it was found that gelatin has the same effect on the lampblack 
as the protein of the blood and that lampblack-gelatin-citrate 
suspensions not only pass through muslin, but even through 
filter-paper. Microscopic examination with the oil-immersion 
lens of the muslin filtrate reveals innumerable rather coarse 
particles together with many minute particles at the limit of 
vision. In the filter-paper filtrate there are no coarse particles, 
but on examination with dark-field illumination innumerable 
ultramicroseopic particles are visible. The lampblack-gelatin- 
citrate suspensious after filtration through the finer filter-papers 
do not separate even after standing a number of days and they 
correspond in all respects to the typical colloid sols. The exact 
way in which gelatin, albumin, and other protective substances 
increase the permanency of colloid solutions is not agreed upon 
by physical chemists. If such a colloid carbon suspension made 
up largely of ultramicroscopic but partly of microscopic particles 
is incubated in vitro with phagocytic cells instead of a suspension 
