2 9 o PROD UCTION AND ABSORPTION OF L YMPH. 
blood pressure below the obstruction. In spite of this fact, the lymph 
flow from the thoracic duct may in some cases be unaltered and even 
slightly increased. 
2. Obstruction of the inferior vena cava above the diaphragm causes 
a general fall of blood pressure, and the intestines become apparently 
an;i'iiiic. The lymph flow from the thoracic duct is largely increased, and 
the lymph undergoes chemical changes, becoming more concentrated 
than it was before the obstruction. This lymph, according to Heiden- 
hain, comes from the intestines, whereas, on obstruction of the portal 
vein, these organs yield an increased flow of a lymph which is less 
concentrated than normal and contains red blood corpuscles. 
3. Heidenhain describes two classes of bodies, which on injection 
into the circulation increase the lymph flow from the thoracic duct. 
The first class comprises bodies such as commercial peptone, watery 
extract of dried leeches or of crayfish. These increase the lymph and 
make it more concentrated. They usually cause a lowering of arterial 
blood pressure, although by careful injection this may be avoided. 
The second class includes crystalloids such as sodium chloride, sugar, 
etc. Injection of concentrated solutions of these bodies into the circula- 
tion evokes an increased flow of lymph which is less concentrated than 
before. Some time after the injection, it is found that the lymph 
contains a greater percentage amount of injected substance than does 
the blood plasma. There may be a slight rise in the arterial pressure, 
but this rise is in no way proportionate to the augmentation in the 
lymph flow. 
Since, therefore, the lymph flow may be increased without any 
corresponding elevation in the blood pressure, and since the amount of 
injected substance in the lymph may rise above that in the blood plasma, 
Heidenhain concludes that the processes of filtration and diffusion are 
incapable of accounting for the changes observed in the amount and 
composition of the lymph ; although he does not deny that, under certain 
pathological conditions, such as heart disease and cirrhosis of the liver, 
dropsy or ascites may be and probably is conditioned by the increased 
intracapillary pressure acting in many cases on a capillary wall already 
weakened and abnormal in consecpuence of anaemic and diseased states 
of the blood. 
Comparison of the theories of Ludwig and Heidenhain. — A 
renewed examination 1 of Heidenhain's experiments, combined with a 
more thorough investigation of their conditions, has persuaded me that, 
so far from overthrowing the filtration hypothesis, they furnish the 
strongest arguments which have yet been adduced in its favour. I may 
therefore give some account of these experiments, and show how they 
support Lud wig's contention with regard to the production of lymph. 
Sources of the lymph investigated. — In dealing with the lymph flow 
from the thoracic duct, it is essential to know from what parts of the 
body this lymph is derived, especially since, as is well known, the 
lymphatics from all parts of the body, with the exception of the 
right upper extremity and right side of the neck, converge to pour 
their contents into this duct. In placing a cannula in the duct, 
in order to collect and measure the lymph, the ducts from the left 
side of the neck and left upper extremity are ligatured. From the 
1 Bayliss and Starling, Joum. Physiol., Cambridge and London, vol. xvi. p. 159 ; Star- 
ling, ibid. vol. xvi. p. 2-2-4, and vol. xvii. p. 30. 
