$10 DR. Il. LYSTER JAMESON ON 
salts secreted and of the periodicity of the secretion as determined 
by the control, or loss of control, of the secreting epidermis. 
In fact, if my interpretation is correct, the processes involved 
in the building of the shell ave the usual chemico-physical ones 
which govern erystallisation in colloidal media * controlled and 
limited by the time-factor which is a function of the activity 
of the living cells. 
It is less easy to imagine the conditions which determine 
the transformation of the fluid albuminous secretion into the 
leathery conchyolin. One is naturally tempted to postulate 
a chemical transformation asa direct or indirect result of the 
action of nascent CaCO,, as in the case of the calcoglobin in 
Harting’s bodies (12); "put the formation of this substance 
apart from the lime-salts, e.g. in the inner layers of the perio- 
stracum and in amorphous repair-substance, and in the case 
of shells grown in lime-free media (Moynier de Villepoix, 28, 
p- 122), seems to negative this; and it may well be that ap 
change to an arial ble albuminoid is directly brought about 
by the action of the secreting cells themselves, or follows from 
the chemical composition of the secretion as shed. 
(12) ABNORMAL AND PaTnoLoGIcAL PHASES OF THE 
SHELL-SUBSTANCE. 
For a study of the beginnings of Ceylon pearls, a consideration 
of the variations in the shell-substance, when it is secreted 
under abnormal conditions, either on the surface of the shell 
or of a growing pearl, is of importance. 
Where the normal rhythm of the process of shell-secretion is 
interrupted, e.g. by injury to the shell, or the intrusion between 
the epithelium and the nacre of a foreign particle or by other 
disturbances less easy to explain, certain irregularities in the 
process of secretion occur, resulting in an alter ed product. 
In the simplest case such a disturbance results in a modification 
producing a granular appearance of the conchyolin-layers of 
the nacre. This modified substance I propose to ‘eal “ granular 
repair-nacre.” In sections made through this substance, after 
decalcification, the normal stratification is obscured by a highly 
granular appearance which seems to be due to an infinite 
number of connections between the successive conchyolin-layers 
resulting in a distinctly alveolar membrane. This is shown 
in text- fig. 38 (repnac.), which is taken from an artificial 
“plister ” produced by the writer in Margaritifera margaritifera 
after the “ Linneus” method, in British New Guinea in 1899. 
The foreign body was inserted near the mantle-margin, and the 
mantle secreted first a double layer of the prismatic subtance, 
* Biedermann (2), p. 171, recognises that the structure of the shell is essentially 
reducible to crystallisation processes, the influence of the cells being limited to the 
composition of the fluid, and perhaps the orientation of the primary centres of 
crystallisation. But I would add to these influences the periodicity of their 
action. 
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