THEORY OF HEIDE XHAIN. 289 
Not so successful were Ludwig's attempts to demonstrate a direct 
relationship between M I pressure and lymph formation. According 
to Ludwig's liypi.ilif.-is, the amount of lymph produced in any given 
part must he proportionate to the difference between the pressure in 
the capillaries and the pressure in the extravascular spaces. In most of 
Ludwig's earlier experiments on the subject this condition was found to 
hold good. On leading defibrinated blood through a limb, the lymph 
production in the limb was Pound proportional to the pressure at which 
the blood was led through it. In the testis Tomsa 1 Bhowed that ligature 
of the pampiniform plexus caused a large increase in the lymph from 
this organ. Paschutin 2 and Emminghaus 3 found that, in the arm and 
leg, extensive ligature of the veins led to an increased lymph production. 
In all these cases, therefore, an augmented flow of lymph was obtained 
by raising the capillary pressure of the part. On the other hand, the 
two last-named observers were unable to prove any constant alteration 
of lymph production incident on vasomotor changes. Thus, in one 
experiment, Paschutin divided the brachial plexus of a dog and then 
stimulated the cut spinal cord, so that there was constriction of all the 
arteries of the body with the exception of those of the fore-limb under 
observation. Even this rise of pressure had no effect 011 the lymph flow 
from the fore-limb. A little later, Kogowicz, 4 working in Heidenhain's 
laboratory, repeated Emminghaus' experiments on the hincl-limb with 
slight alterations, and found almost invariably a slight increase in the 
lymph after section of the sciatic nerve or in consequence of active vaso- 
dilatation. He proved, moreover, that the vaso-dilatation of the tongue 
produced by excitation of the Ungual nerve was followed by an increased 
lymph production in the tongue, which might at times amount to an 
actual unilateral oedema of this organ. 
Theory of Heidenhain. — In dealing with the laws affecting 
lymph production, we are hampered by the fact that, from the limbs 
of an animal at rest, there is, under normal conditions, no lymph flow 
at all, so that, when we wish to study the effects of our various 
procedures on the lymph production in the limb, we have artificially 
to bring about a lymph flow by kneading and massaging the limb. 
This fact introduces at once an arbitrary element into the observa- 
tion, and Heidenhain suggested, therefore, that the best mode of 
investigating the truth of the filtration hypothesis would be to 
experiment on the lymph flow from the thoracic duct. This physio- 
logist carried out a long research on the various conditions under 
which the lymph flow from the thoracic duct might be increased 
or di mini shed, 5 and came to the conclusion that the results of his 
experiments were irreconcilable with the filtration doctrine, and that we 
must assume that the cells forming the walls of the capillaries take an 
active part in lymph formation, i.e. that lymph must be looked upon as 
a secretion rather than as a transudation. A very similar conclusion had 
been previously arrived at by Tigerstedt, 6 mainly on theoretical grounds. 
Heidenhain's arguments may be shortly summarised as follows : — 
1. Obstruction of the thoracic aorta causes a general fall of arterial 
1 Sitzungsb. d. k. Akad. d. Wissensch., Wien, 1862, Bd. xlvi. S. 185. 
2 Arb. a. d. physiol. Anst. zu Leipzig, 1873. 8 Ibid., 1873. 
4 Arch./, d. ges. Physiol., Bonn, 1885, Bd. xxxvi. S. 252. 
5 Ibid., 1891, Bd. xlix. S. 209. 
6 Mitih. a. d. physiol. last, zu Stockholm, 1886. 
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