“The study of F.A.M. Wiggermann on protective spirits has contributed considerably to the understanding of the apkallus in Bīt Mēseri.
(Wiggermann, Mesopotamian Protective Spirits; Wiggermann deals with Bīt Mēseri especially on p. 105f. The connection between the apkallus and prophylactic rituals was already noticed by Oliver Robert Gurney, “Babylonian Prophylactic Figures and their Rituals,” Annals of Archeology and Anthropology 22, Liverpool University Press, 1935, pp. 35-96.)
In Bīt Mēseri it is clear that there is already a sick man in the house. The ritual prescribes both how paintings of protective figures and small statues of them should be placed in the room of the sick man, and what incantations should be used. The ritual should be performed by the āšipu, the magician or exorcist operating against evil spirits causing diseases.
Three kinds of apkallus are also represented in Bīt Mēseri: ūmu-apkallus, fish-apkallus, and bird-apkallus. The designation ūmu can mean both “light” and “day;” Wiggermann opts for the second solution; they are “day-apkallus.”
The fish-apkallus and the bird-apkallus are bīnūt apsê, “creatures of apsû.” They have divine origin.
Nothing similar is said about the day-apkallus. They seem to be of human descent. Nevertheless, Wiggermann considers them to have their origin from the antediluvian period as well.
The instructions concerning the invocation of the apkallus are introduced in the following way in Bit Meseri:
“To the seven figures of carp apkallus, painted with gypsum and black paste that are drawn at the side of the bedroom at the wall.
To the seven figures of apkallus of consecrated cornel; they stand in the gate of the bedroom nearest the sick man at the head of the bed.
To the seven figures of apkallus of tamarisk, kneeling, that stand at the foot of the bed.”
Thus, protective spirits surrounded the sick man. The first group is fish-apkallus, which is explicitly mentioned; the second is day-apkallus, on the basis of the material used; most likely the third is the bird-apkallus.
The list of seven and the subsequent four apkallus that we have been dealing with come after the first invocation. We therefore notice that these apkallus are fish-apkallus, which also is apparent in the description of them in the list. There is, however, an incongruity between the invocation and the list.
The invocation deals with seven apkallus; the list has in total eleven. This seems to indicate that the list is adapted into the ritual from another source.”
Helge Kvanvig, Primeval History: Babylonian, Biblical, and Enochic: An Intertextual Reading, Brill, 2011, p. 131.