4. ANALYSIS O F FACTORS INVOLVED IN SYMBIOSIS
79
immobilizing substance in Australorbis glabratus, Michelson (1963a) has
cautiously stated that :
Although the suggestion that the immobilizing phenomenon might be
associated with an antigen-antibody is an appealing one, data are lacking
to substantiate this hypothesis. The possibility that the immobilizing
substance(s) might be related either to parasite-produced toxins or to
products resulting from alterations in the snail’s metabolism cannot be
excluded.
It is of interest, nevertheless, to speculate as to why Michelson’s
miracidia-immobilizing substance is only found in tissue extracts and
not in plasma. One possible explanation is that these factors are either
located intracellularly, or, more likely, adhere to the surfaces of cells
and can only be detected after the cells are disrupted or ruptured
during the extraction process. As a final word, Michelson’s speculation
that it may be a parasite-produced toxin or a product resulting from
alterations in the snail’s metabolism certainly cannot be overlooked,
especially since it is known through the works of Faust (1917), Agersborg (1924), Hurst (1927), Cheng and Snyder (1962a), and Cheng and
Burton (1965b) that there is, among other pathological changes, an
increase of so-called ferment cell secretions in molluscs parasitized by
trematodes. Hurst has attributed a “ lytic ” activity to these secreted
globules. Although Cheng and Burton (1965a) have pointed out that
there is no direct evidence for Hurst’s contention, a t the same time
there is no direct evidence to the contrary. Thus, these globules,
among many possibilities, may represent a “ toxin ” which could be
manifested as an immobilizing factor. At any rate, much remains to be
studied relative to both cellular and humoral defense mechanisms in
molluscs.
I n addition to the small yellowish ferment cell secretions, another
type of cell, commonly referred to as “ brown cells ” (Takatsuki, 1934),
“ das rotbraunes organ ” (Keber, 1851), or cells of “ Keber’s organ ”
(Fernau, 1914), are known t o increase in number in parasitized oysters
and other pelecypods. These cells are believed to have their origin in
the darkened areas on the mantle, in the pericardium, in connective
tissues, but primarily on the surface of the auricles (see reviews by
White, 1942 ; GrassB, 1960). They are also known to undergo mitotic
division in tho Leydig tissues of oysters (Cheng and Burton, 1965b).
The function of “ brown cells ” has not been demonstrated experiment d l y although Mackin (1951, 1962) and Stein and Mackin (1955) have
suggested that their function is associated with the internal defense
mechanisms of oysters since they have found a correlation between the
increase in number of “brown cells” and infection by the fungus
79
immobilizing substance in Australorbis glabratus, Michelson (1963a) has
cautiously stated that :
Although the suggestion that the immobilizing phenomenon might be
associated with an antigen-antibody is an appealing one, data are lacking
to substantiate this hypothesis. The possibility that the immobilizing
substance(s) might be related either to parasite-produced toxins or to
products resulting from alterations in the snail’s metabolism cannot be
excluded.
It is of interest, nevertheless, to speculate as to why Michelson’s
miracidia-immobilizing substance is only found in tissue extracts and
not in plasma. One possible explanation is that these factors are either
located intracellularly, or, more likely, adhere to the surfaces of cells
and can only be detected after the cells are disrupted or ruptured
during the extraction process. As a final word, Michelson’s speculation
that it may be a parasite-produced toxin or a product resulting from
alterations in the snail’s metabolism certainly cannot be overlooked,
especially since it is known through the works of Faust (1917), Agersborg (1924), Hurst (1927), Cheng and Snyder (1962a), and Cheng and
Burton (1965b) that there is, among other pathological changes, an
increase of so-called ferment cell secretions in molluscs parasitized by
trematodes. Hurst has attributed a “ lytic ” activity to these secreted
globules. Although Cheng and Burton (1965a) have pointed out that
there is no direct evidence for Hurst’s contention, a t the same time
there is no direct evidence to the contrary. Thus, these globules,
among many possibilities, may represent a “ toxin ” which could be
manifested as an immobilizing factor. At any rate, much remains to be
studied relative to both cellular and humoral defense mechanisms in
molluscs.
I n addition to the small yellowish ferment cell secretions, another
type of cell, commonly referred to as “ brown cells ” (Takatsuki, 1934),
“ das rotbraunes organ ” (Keber, 1851), or cells of “ Keber’s organ ”
(Fernau, 1914), are known t o increase in number in parasitized oysters
and other pelecypods. These cells are believed to have their origin in
the darkened areas on the mantle, in the pericardium, in connective
tissues, but primarily on the surface of the auricles (see reviews by
White, 1942 ; GrassB, 1960). They are also known to undergo mitotic
division in tho Leydig tissues of oysters (Cheng and Burton, 1965b).
The function of “ brown cells ” has not been demonstrated experiment d l y although Mackin (1951, 1962) and Stein and Mackin (1955) have
suggested that their function is associated with the internal defense
mechanisms of oysters since they have found a correlation between the
increase in number of “brown cells” and infection by the fungus