A STUDY OF THE STRUCTURAL UNIT OF THE LIVER. 
BY 
FRANKLIN P. MALL. 
From the Anatomical Laboratory of the Johns Hopkins University. 
WitH 74 FIGURES AND 7 TABLES. 
In studying the structural development of an organ it is necessary to 
consider the systems within it as a whole and to determine their relations 
to one another. Analytical methods, which must precede synthetical 
methods, have shown that organs are built up of like parts, or structural 
units, which are analagous to the leaves of a tree. However, in the growth 
of an organ the units are not thrown off annually, but are gradually 
shifted and transformed into new units. It follows that in a study of 
the kind proposed it is always necessary to consider the unit in relation 
to the organ as a whole throughout its development, and to do this we 
must constantly resort to reconstruction. Of course this cannot be done 
with much success, in the ordinary sense of the term, but for the present 
purpose, the tables may be considered as reconstruction. Geologists, geog- 
raphers, archwologists and anatomists each have their own methods of 
reconstruction, and I have utilized them all, more or less, in the present 
study. 
I undertook the study of the structural development of the liver on 
account of its well-known and sharply-defined lobule. It was thought at 
the beginning that this lobule was the simplest of all the structural units 
and therefore the most suitable for a study of this kind. It soon became 
evident that the lobule was not the structural unit, and that both lobules 
and units were extremely difficult to follow in their development, for they 
are constantly blended with adjacent lobules, or units as the case may be. 
Furthermore, lobules or units once formed do not remain, but sprout, 
fracture and rearrange themselves, thus making the various pictures ob- 
tained complex and difficult to interpret. 
The work has been carried on during a number of years, after being 
laid aside in order to take up the same question in other organs. 
These secondary studies,—usually made by others connected with me,— 
have aided my work for the liver materially, which I now venture to 
present in a more or less connected form. 
AMERICAN JOURNAL OF ANATOMY.—VOL. V. 
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