LYMPHATICS. 
161 
tem. The tenuity of the walls of these vessels, even in their 
course, and the presence of innumerable valves, renders it im¬ 
possible to study them by the ordinary methods of injection. 
Yet it has been ascertained and positively proved by the in¬ 
jection of a solution (generally of mercury), gently diffused 
into the vessel of origin and following the vessels as the fluid 
follows their course, into the larger trunks, and thence to the 
lymphatic glands, and the regularity with which the minute ves¬ 
sels carry their burden through to the larger vessels the glands, 
proved that the lymphatics have been penetrated, and that 
the appearances observed are not the result of mere infiltra¬ 
tion. The mode of origin of the finest vessels in the lympha¬ 
tic radicles is exceedingly obscure, notwithstanding the nu¬ 
merous investigations which have been made within the last 
few years, particularly by the German anatomists. In fact, 
the lymphatics have not been actually injected and demon¬ 
strated in all the tissues of the body ; yet because we have 
not been able to inject them we are not justified in assuming 
positively that they do not exist, for example, in the intestinal 
villi. According to Sappey, they have never been seen, al¬ 
though we have no doubt of their existence. 
In the elaborate observations made by Dr Belaiff, of St. 
Petersburg, speaking of the origin of the lymphatics of the 
penis, the walls of the vessels were made apparent by the ac¬ 
tion of nitrate of silver in solution in pure water, and it is 
probable that they were very little distended, for the smallest 
of these vessels had a diameter of about one three-hundredths 
of an inch. 
Robins and his associates have seen found a curious sys¬ 
tem of vessels which inhabit the brain and spinal cord, entire¬ 
ly surrounding the capillary blood vessels, and connected 
with the lymphatic trunk or reservoir, described by Fohman, 
under the piamater. These capillary vessels float in a fluid 
contained in cylindrical sheaths, which exceed them in diam¬ 
eter by from one twelve-hundredth to one four-hundredth of 
an inch, the investing vessels following the blood vessels in 
their ramifications and containing a clear fluid with bodies re¬ 
sembling the lymph corpuscles. When Robins first described 
