3 1 o PROD UCTION AND ABSORPTION OF L J 'MPH. 
the serum will tend to become gradually weaker, so that the watery 
and saline constituents corresponding to the proteid used up can then 
be absorbed by the blood vessels in the way I have indicated. 
The physical process which I have described above as causing the 
absorption of lymph by the blood vessels must be in action at all times 
in the body, and must therefore be a predominant factor in the process of 
absorption. I have not been able to absolutely exclude the absorption 
of proteids by the blood vessels, but, in the absence of direct experi- 
mental evidence that such an absorption does occur, the physical factors 
I have described in this chapter suffice to explain the phenomena of 
absorption observed both under normal and under pathological conditions. 
On the Functions of the Lymph in the Nutrition of 
the Tissues. 
The fact that the tissue cells are bathed by lymph and are 
separated by this fluid and by the capillary wall from the blood, 
shows that hi all interchanges between blood and tissues the lymph 
must act as the medium of communication. 
I have already mentioned the irrigation theory of Bartholin, accord- 
ing to which the nutrition of the tissues was carried out by a taking up 
of solids from the lymph as it left the blood vessels, so that only pure 
water (or water and salts — Eudbeck) was left over to be carried away 
by the lymphatics. 
The observations of the Ludwig school on the lymph flow from the 
limbs, showed clearly, however, that the nutrition of the tissues could 
be normally carried out without any lymph flow at all. The muscles 
of a resting limb are taking up nourishment as well as oxygen from the 
blood, and giving off their waste products, carbonic acid and ammonia, 
although not a drop of lymph may now from a cannula placed in a 
lymphatic trunk of the limb. It is evident, therefore, that to a large 
extent, at any rate, the giving up of nourishment by blood to tissues and 
the taking up of the waste products of the latter through the inter- 
mediation of the lymph, is carried out in the same way as are the gaseous 
interchanges — i.e. by a process of diffusion. 
I have already mentioned the experiments which demonstrate the 
extreme rapidity with which diffusion takes place between the blood and 
the lymph, so that, as Leathes points out, the time taken for the 
equalisation of the constitution of the two fluids after introduction of 
some diffusible substance into the blood is " inappreciable." There can 
be no doubt that such changes are of great importance for the normal 
metabolism of the tissues. Thus there has been considerable discussion 
of late years concerning the supply of lime to the cells of the mammary 
gland. Heidenhain pointed out that if the lime were supplied to the cells 
by filtration, the whole flow from the thoracic duct would be inadequate 
for the purpose. His conclusion that the lymph with its constituents i- 
therefore a secretion is, however, unnecessary. As the gland cell uses 
up or turns out lime into the duets of the gland, it will take up lime 
from the adjoining lymph, thus lowering the partial osmotic tension of 
the lime in its neighbourhood. There will be, therefore, a passage of 
lime from blood to lymph by a process of diffusion, to supply the 
deficiency. Xo flow of lymph at all is necessary to furnish the amount 
of lime required by the gland cell. 
