192
M. A B E R C R O M B I E
1954) particularly because of the long-lasting adhesions that link fibroblasts to each other. Mutual negative chemotaxis, such as described for
amphibian melanoblasts by Twitty and Niu (1948, 1954), will of course
have the same effect.
A cell may be trapped also, and this may be regarded as an extreme
of an unoriented response, when it comes to adhere so closely to its
surroundings that it is anchored in place. Coman (1953) has developed
an important theory of the mobility of cancer cells based on the idea
that normal cells are immobilized by mutual adhesion. An instance
investigated in tissue culture is the immobilization of Schwann cells by
adhesion to axons (Abercrombie, Johnson and Thomas, 1949). Finally,
speed may no doubt be reduced to zero by change in concentration of
something in the liquid medium. Trevan and Roberts (1960) have
described how exhaustion of the medium may result in the disappearance of all signs of movement in cultured epithelioma ascites cells, with
consequent predominance of mutual adhesion; a state which is reversible by feeding.
The starting up of movement in a stationary cell can be regarded
simply as release from the mechanisms of immobilization discussed.
There is a special interest for tissue culture in the initiation of emigration from a fresh explant, which usually occurs after a latent period of
at least several hours. Contact inhibition is not involved in the latent
period, since the act of explanting releases the peripheral cells of the
fragment from such inhibition. The effectiveness of whatever the temporary immobilizing factor is can be varied by pretreatment in vivo of
the tissue. The induction of proliferation before explantation shortens
the latent period and increases the subsequent rate of emigration, as
Loeb (1912) seems to have been the first to report. Similar differences
in latent period and subsequent rate of emigration are found when a
tissue is explanted from donors of different ages; roughly, young donors,
with high multiplication rates, have their cells ready mobilized to a
greater degree than have old donors, though the correlation is not
perfect (Goldschmidt, Hoffman and Doljanski, 1937; Doljanski,
Palevitsch and Goldschmidt, 1940; Cohn and Murray, 1925; Olivo,
1928; Lefford, 1963). Malignant tumours similarly may have short
latent periods (see for instance Doljanski and Halberstaedter, 1937).
Trypsin treatment of explants also reduces the latent period (Simms
and Stillman, 1937; Lefford, 1963). These problems of the mobilization
of "resting" cells, and the converse, have been discussed by Abercrombie
and Ambrose (1962); it is evident that in vivo a complex of different
processes is involved.
M. A B E R C R O M B I E
1954) particularly because of the long-lasting adhesions that link fibroblasts to each other. Mutual negative chemotaxis, such as described for
amphibian melanoblasts by Twitty and Niu (1948, 1954), will of course
have the same effect.
A cell may be trapped also, and this may be regarded as an extreme
of an unoriented response, when it comes to adhere so closely to its
surroundings that it is anchored in place. Coman (1953) has developed
an important theory of the mobility of cancer cells based on the idea
that normal cells are immobilized by mutual adhesion. An instance
investigated in tissue culture is the immobilization of Schwann cells by
adhesion to axons (Abercrombie, Johnson and Thomas, 1949). Finally,
speed may no doubt be reduced to zero by change in concentration of
something in the liquid medium. Trevan and Roberts (1960) have
described how exhaustion of the medium may result in the disappearance of all signs of movement in cultured epithelioma ascites cells, with
consequent predominance of mutual adhesion; a state which is reversible by feeding.
The starting up of movement in a stationary cell can be regarded
simply as release from the mechanisms of immobilization discussed.
There is a special interest for tissue culture in the initiation of emigration from a fresh explant, which usually occurs after a latent period of
at least several hours. Contact inhibition is not involved in the latent
period, since the act of explanting releases the peripheral cells of the
fragment from such inhibition. The effectiveness of whatever the temporary immobilizing factor is can be varied by pretreatment in vivo of
the tissue. The induction of proliferation before explantation shortens
the latent period and increases the subsequent rate of emigration, as
Loeb (1912) seems to have been the first to report. Similar differences
in latent period and subsequent rate of emigration are found when a
tissue is explanted from donors of different ages; roughly, young donors,
with high multiplication rates, have their cells ready mobilized to a
greater degree than have old donors, though the correlation is not
perfect (Goldschmidt, Hoffman and Doljanski, 1937; Doljanski,
Palevitsch and Goldschmidt, 1940; Cohn and Murray, 1925; Olivo,
1928; Lefford, 1963). Malignant tumours similarly may have short
latent periods (see for instance Doljanski and Halberstaedter, 1937).
Trypsin treatment of explants also reduces the latent period (Simms
and Stillman, 1937; Lefford, 1963). These problems of the mobilization
of "resting" cells, and the converse, have been discussed by Abercrombie
and Ambrose (1962); it is evident that in vivo a complex of different
processes is involved.