FUNCTIONS OF THE L YMI'll. 3 1 1 
The case is rather differenl when we come to consider the supply of 
proteid food to the tissues. The diffiisibility of the large molecular 
serum proteids is so small that it may be disregarded, even in the 
living body with its wonderfully perfect arrangement for allowing the 
free contact of fluids without hiterminghng. Hence the only way by 
which the tissues can obtain their supply of proteid is from the proteid 
which has filtered through the vessel wall in the lymph. So far as the 
proteid supply to the tissues is concerned, therefore, I believe that the 
irrigation theory is correct, unless, indeed, we attribute to the vascular 
epithelium the power of actively taking up proteid and transferring it 
from one side of the vessel wall to the other in proportion to the needs 
of the tissues. 
Even under the former hypothesis, however, we could not, from the 
amount of lymph draining away from a part, draw any conclusions as to 
the amount of proteid which has been supplied to the part. As I 
have above shown, the (-(imposition of the lymph is determined by the 
permeability of the wall and the mean capillary pressure. If the com- 
position of the lymph be altered after transudation, in consequence of 
an active using up of the proteids of the tissue cells, the effective 
osmotic difference between blood and lymph will be increased, and the 
watery and saline constituents of the lymph will be reabsorbed until the 
original constitution of the lymph is restored. 
We may conclude, therefore, in default of definite evidence to the 
contrary, that while the interchange between tissues and blood, so far as 
diffusible substances are concerned, is effected by diffusion through the 
medium of the lymph, the proteid supply to the cells is dependent on 
the amount of proteid transuding with the lymph. 
Perhaps it is on this account — i.e., increased proteid supply to the 
cells — that chronic inflammation or hyperemia of any part is apt to lead 
to its hypertrophy. Growing tissues, as well as those in a state of repair, 
have delicate vessels, which probably supply a lymph much richer in 
proteids than is supplied to adult tissues. 
