304 

NATURE 
+ oe 
[Marcu 3, 1923 
The Unit Activity of Animal Organs. 
NE of the most remarkable features of the 
animal body is the fact that each organ has 
more substance than is necessary to do its normal 
amount of work. Teleologically it is easy to see that 
some such arrangement is necessary for successful 
survival, but it is more difficult to imagine the 
mechanism by which it is kept in working order. 
If a muscle is used less it grows smaller, and if it is 
used more it grows larger. In each case it preserves 
the margin of power which is known as “ reserve 
force,’’ despite the definite general relation between 
quantity of substance and quantity of function. In 
a recent number of the Jouynal of Pathology and 
Bacteriology (vol. xxv. p. 414) Dr. V. R. Khanolkar 
makes some interesting speculations and observations 
which seem to throw light on the problem, and he 
extends them into suggestions which may clear up 
some obscure points in respect of the distribution 
of pathological lesions in organs. So long ago as 
1871 Bowditch formulated the proposition that if the 
frog’s heart responds at all to an artificial stimulus 
it responds with the greatest contraction of which 
the muscle is at the time capable. This principle 
of “all or nothing’’ has since been extended to 
other excitable tissues, most convincingly to muscle 
and nerve, and by implication to glands which receive 
their normal stimuli through the nervous system. 
On this basis, moderate activity of a skeletal muscle 
means maximal activity of a moderate number of 
the units, in this case muscle fibres, of which it is 
made up and not moderate activity of all the units. 
In other words, in ordinary circumstances only a 
proportion of the units of any organ are active at 
any one time. How then do the other units escape 
the consequences of the rule that tissue which is not 
used atrophies and disappears? Marey in 1885 
found that the responsivity of the frog’s heart to 
external stimuli is least when it is actually contracting 
and is only gradually restored to normal after the 
contraction is over. Each period of activity is thus 
followed by a “‘ refractory period” in which the tissue 
will not respond to a strength of stimulus which 
would normally rouse it to activity, the resistance to 
excitation fading away until the normal excitability 
is regained. This refractory phase has been closely 
studied in nerve muscle and sense organs, and Gotch 
described it as a general phenomenon of living sub- 
stance. In this way a rotation of activity among the 
units of any organ is brought about : with moderate 
activity in response to moderate stimulation a 
proportion of the units are constantly in action, but 
as the refractory period of each one comes on it 
stops working and its function is taken on by another 
unit with its activity more remote and its refrac- 
tory period completed. As the activity of the whole 
organ is increased owing to stronger stimulation, the 
refractoriness of units is broken through first in 


those the activity of which is remote, next in those 
which have functioned more recently. Finally, with 
maximal stimulation all the units are forced into 
simultaneous action. 
It seems likely that a rinciples, elucidated 
by the classical method of “ wiring frogs on to 
machinery,”’ are applicable to other tissues in which 
their demonstration is more difficult. What con-— 
stitute anatomical “‘ units’ is not known. In nerve 
and muscle they are the individual fibres, in the 
central nervous system probably nerve cells, in the 
kidney possibly the glomerular-tubal systems, in 
glands apparently groups of adjacent cells—but they 
might be parts of organs, cells, or even parts of cells. 
Dr. Khanolkar has specially concerned himself with 
the kidney, and supposing that each glomerulus 
with its efferent tubule is a unit, points out that the 
hypothesis would explain the irregular distribution 
of the lesions in the common chronic degeneration 
of that organ. Assuming that the original inju 
is due to some poison circulating in the blood, it 
follows that more of it will reach active than passive 
units since activity is always associated with a local 
increase in blood supply. On general grounds also 
it is quite likely that functioning cells are more 
reactive and hence more easily poisoned than cells 
at rest. In chronic general nephritis some glomeruli 
are destroyed while others appear to escape injury — 
altogether, and the diseased and healthy units are 
found scattered uniformly all over the organ. It is 
suggested that the injured units are those which 
happened to be active when a toxic concentration 
of the poison was in the blood. Extending the idea 
to other organs, it follows that activity always renders 
a tissue more susceptible to poisonous substances, 
which may be the explanation of why the parts 
of the nervous system most constantly in heavy use 
are specially liable to suffer in general lead poisoning 
and other similar relations. Failure of an organ 
from over use might in part be due to this, in part 
to the absence of rest for any of the units. It is well 
recognised that hypertrophy of skeletal muscle is 
best secured by exercises which seem absurdly mild : 
on the hypothesis of unit activity it is easy to under- 
stand why light dumb-bells should keep more units 
in the best possible condition than heavy ones. 
Dr. Khanolkar adduces experimental evidence that 
in the kidney during moderate activity only some 
of the glomeruli are in action, while more or all will 
excrete actively when the organ is strongly stimulated 
with diuretics. Incidental observations on the 
adrenal medulla, pituitary, pancreas, and salivary 
glands give histological evidence of the same partial 
activity. The whole fits in well with Krogh’s recent 
demonstration that many capillaries in normal 
organs are at any one moment closed and out of 
action. 
Climates of the Past. 
W R. ECKARDT, of Essen, has contributed a 
* memoir, ‘‘ Palaoklimatologie, ihre Methoden 
und ihre Andwendung auf die Palaobiologie,’’ to 
Prof. Abderhalden’s comprehensive ‘‘ Handbuch der 
biologischen Arbeitsmethoden”’ (Urban und Schwarzen- 
berg, Berlin), of which it forms Heft 3 of Abteilung 
ro. It is written in what may be called the tiber 
Alles type of German, without much consideration 
NO. 2783, VOL. 111] 
for the southerner or the stranger, and sentences 
containing more than 100 words are not uncommon. 
It embodies, however, a valuable and critical review 
of the way in which various classes of geological 
evidence may be used as indications of the climatic - 
environment of the faunas and floras of the past. 
The character and colour of fossil soils are discussed 
by Dr. Eckardt, equally with the distribution of 
