Experimental Methods II. The Defect Closure Rule - Tissue and Organ Regeneration in Adults - page 81

assumed identical to that of the corresponding entry for C . All entries in the table
other than contraction data were calculated or estimated by the author based on
contraction data and qualitative evidence reported by the investigators. Remodeling
effects were neglected in Table 4.3 .
Inspection of the data in Table 4.3 shows that the relative contributions of scar
and contraction vary extensively with the species. The data quantitatively state the
well-known fact that contraction makes a much larger contribution to defect clo-
sure in adult rodents than in the human or the swine. In the rodent (rat, mouse), as
well as in the rabbit, classified as a lagomorph rather than a rodent (Goss 1980),
the contraction term is about nine times as large as the scar formation term. If we
take C >> S , we get a rough approximation for the closure rule in the rodent and the
rabbit:

(4.3)

C ≈ 100 (several adult rodents; adult rabbit)

It follows that, to the rough approximation of Eq. 4.3, the configuration of the fi-
nal state in the rodents and lagomorphs is approximately [100, 0, 0]. We are not
aware of comparable data on mammalian fetal healing in the literature. However,
the available evidence with skin defects in certain early gestation fetal models has
led authors to the qualitative conclusion that scar formation and contraction make
negligible contributions to defect closure in the early mammalian fetus (see reviews
by Mast et al. 1992b; McCallion and Ferguson 1996; Estes et al. 1994; Beanes et al.
2002; Soo et al. 2003), referred to below as the “idealized” fetal model. This sug-
gests that C = S = 0, and, therefore, the simple approximate result follows:

(4.4)

R = 100 (idealized fetal model, skin)

The final state configuration for the fetal model is [0, 0, 100]. In an adult human,
where the evidence (Ramirez et al. 1969) shows that R = 0, and contraction contrib-
utes approximately as much as does scar formation, we have the rough approxima-
tion represented by Eq. 4.5:

(4.5)

CS (adult human, skin)

Certainly very useful quantitative conclusions, most of them well known as qualita-
tive statements, emerge from the defect contraction data of Table 4.3 . The dermis-
free defect in the guinea pig, rabbit, rat, and mouse closes largely by contraction of
a “fully mobile integument” (Billingham and Medawar 1951, 1955). Contraction
contributes less to closure in adult porcine skin than in rodents (Rudolph 1979).
In the rabbit, the tissue immediately underneath the dermis consists of several thin
layers of connective tissue (superficial fasciae). In the guinea pig, the layer of tissue