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F. Ε. LEHMANN
increase of cathepsin activity in corresponding circumstances. Benz
(1959) has demonstrated, after having investigated many rats, that
there is in fact a relation between tumour-size and the cathepsin activity
of some organs. This relation comes into play only after the tumour
weight has reached 1% ofthat of the whole host after complete bleeding.
Smaller tumours seem to have no significant effect. Therefore the increase
in cathepsin activity is very evident in animals with large tumours
(10-20% of the body weight). Tumours of the Walker Carcinoma
produce such effects in rats as do the large tumours of T8-G-Epithelioma.
Tumours of adenocarcinoma EO 771 induce an analogous increase of
the cathepsin activity in liver and kidney of mice.
This remarkable phenomenon of increased catheptic activity in some
organs of tumour-bearing mammals seems more understandable if one
considers the whole protein balance in a mammal. The growing tumour
traps many essential amino acids because its necrotic material does not
return to the general protein reserves. The protein of the normal organs
are now mobilized and furnish their own amino acids to the proteinconsuming parts of the tumour via the serum proteins. An implanted
tumour may grow in a first phase without great general effect on the
host as long as its requirements are covered by the proteins of the food.
In the subsequent second phase the situation will change as soon as
the protein level of the blood, which functions as a general protein
reserve, becomes exhausted. This will induce mobilization of reserve
proteins in some organs especially in the muscle as during starvation.
A significant increase of catheptic activity in these organs will take
place and is easy to observe. The second phase of tumour-induced
starvation and organ breakdown causes further foreign break-down
products to appear in the blood and to be taken in by pinocytosis of
some organs. This increased pinocytosis leads to a hypertrophy of the liver
and the kidney often observed under those circumstances. At the same
time the catheptic activity of the same organs increases. All the phenomena, found until now during the second phase of tumour growth, can
be explained on the basis of our assumption of the central role of the
protein turnover in the host organism.
In the third phase the tumour is growing more slowly but its protein
parasitism is now reinforced. Fragments of host proteins seem to be
principally consumed. The need for proteins within the tumour can no
longer be covered by the host. The starvation of the animal increases.
The body loses weight, the animal shows little tendency to feed sufficiently and the food intake regresses and a great amount of nitrogen is
excreted in the urine. The increased catheptic activity in all organs
indicates an increased proteolysis in order to maintain the protein level
of serum, which is utilized by the steadily growing tumour. It seems
F. Ε. LEHMANN
increase of cathepsin activity in corresponding circumstances. Benz
(1959) has demonstrated, after having investigated many rats, that
there is in fact a relation between tumour-size and the cathepsin activity
of some organs. This relation comes into play only after the tumour
weight has reached 1% ofthat of the whole host after complete bleeding.
Smaller tumours seem to have no significant effect. Therefore the increase
in cathepsin activity is very evident in animals with large tumours
(10-20% of the body weight). Tumours of the Walker Carcinoma
produce such effects in rats as do the large tumours of T8-G-Epithelioma.
Tumours of adenocarcinoma EO 771 induce an analogous increase of
the cathepsin activity in liver and kidney of mice.
This remarkable phenomenon of increased catheptic activity in some
organs of tumour-bearing mammals seems more understandable if one
considers the whole protein balance in a mammal. The growing tumour
traps many essential amino acids because its necrotic material does not
return to the general protein reserves. The protein of the normal organs
are now mobilized and furnish their own amino acids to the proteinconsuming parts of the tumour via the serum proteins. An implanted
tumour may grow in a first phase without great general effect on the
host as long as its requirements are covered by the proteins of the food.
In the subsequent second phase the situation will change as soon as
the protein level of the blood, which functions as a general protein
reserve, becomes exhausted. This will induce mobilization of reserve
proteins in some organs especially in the muscle as during starvation.
A significant increase of catheptic activity in these organs will take
place and is easy to observe. The second phase of tumour-induced
starvation and organ breakdown causes further foreign break-down
products to appear in the blood and to be taken in by pinocytosis of
some organs. This increased pinocytosis leads to a hypertrophy of the liver
and the kidney often observed under those circumstances. At the same
time the catheptic activity of the same organs increases. All the phenomena, found until now during the second phase of tumour growth, can
be explained on the basis of our assumption of the central role of the
protein turnover in the host organism.
In the third phase the tumour is growing more slowly but its protein
parasitism is now reinforced. Fragments of host proteins seem to be
principally consumed. The need for proteins within the tumour can no
longer be covered by the host. The starvation of the animal increases.
The body loses weight, the animal shows little tendency to feed sufficiently and the food intake regresses and a great amount of nitrogen is
excreted in the urine. The increased catheptic activity in all organs
indicates an increased proteolysis in order to maintain the protein level
of serum, which is utilized by the steadily growing tumour. It seems