ABSTRACT
In accordance with expectation, the embryonic chick heart exposes recurrently temperature characteristics of the orders 8,200, 14,200, 16,400, 18,300, 20,500 and 25,200. These are found in both myogenic and neurogenic hearts but not with the same frequencies. These two periods of development also differ in the localisation of critical points. So far μ. = 8,200, 14,200 and 18,300 have been exposed in embryos only by Fundulus’, the remaining three orders however are recurrent also in the embryogeny of Limulus. Two orders not included in this list (5000 and 11,000) are rare, yet, even so, not restricted to any one of the three forms. These facts, together with their implications, suggest for heart rhythm in Limulus, Fundulus and the Chick, an underlying physical-chemical mechanism in structure identical for all three types of heart at all stages of development, and differing in neurogenic stages only by a revision of the myogenic time relations.
These analyses rest on the fact that the equation ln
, properly applied, gives an accurate description and objective reproduction of the data. For closeness of fit, see Glaser 1924, 1925 and 1929.
The velocity constants and K1 and K0 inversely proportional to the time required per beat at the absolute temperatures T1 and To. R is the gas constant and μ a factor designated by Crozier (1924 a, b) as the temperature characteristic or critical thermal increment and accounting for changes of rate associated with changes of temperature.
In the graphs μequals slope, but physically and in theory it represents the energy required by a given species of molecule when transforming from the chemically inactive to the reactive state.
A biological process is attributable to a series of underlying chemical reactions linked in definite sequence. Ordinarily such catenary systems can proceed no faster than the component with the slowest rate of acceleration. This is the controlling rate, and in a complicated system is the only one of which μ is a measure. Hence constant and recurrent values of μ implicate constant, recurrent ami specific chemical reactions.
