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Physiology and the whole organism  ·  Article

Differential susceptibility as a measure of metabolic rate

Differential susceptibility was a method used by C. M. Child to compare regions of an organism. Child related susceptibility to the rate of metabolism or oxidation, and used it to demonstrate metabolic gradients.12 Child did not claim that the relation holds in every case.4 The method also served to modify development, so it was more than a measuring tool.8

Earliest held
1915, Child, C. M.
Most discussed in
Physiological Foundations of Behavior, 1924
In the library
47 passages in 3 works
Rewritten
2026-10-09
18501875190019251950197520002025Child, C. M., 19151Child, C. M., 19152Child, C. M., 19153Child, C. M., 19214Child, C. M., 19215Child, C. M., 19216Child, C. M., 19247Child, C. M., 19248Child, C. M., 19249
01

Gradients by two methods

In Individuality in Organisms (1915), Child cited Tashiro's 1913 method for estimating very small amounts of carbon dioxide. The region of highest carbon dioxide production was taken to be the region of highest respiratory rate. Child argued that oxidations are of fundamental importance in the metabolic reaction system. On that ground, carbon dioxide estimates led to the same conclusions about metabolic gradients as the susceptibility method did.1

02

The penetration objection

Child addressed a possible objection to the susceptibility method. In Tubularia, all of the stem except the cut end is covered by a horny perisarc. A reagent might therefore enter chiefly from the cut end. The resulting death gradient would then be a gradient of penetration and would not represent metabolic conditions.3 Child held that Corymorpha avoids this objection, because most of its stem is naked. The metabolic relations of its parts to the gradients were essentially the same as in Tubularia.2

03

Limits of the claim

In The Origin and Development of the Nervous System (1921), Child stated the claim narrowly. The conclusions about susceptibility and rate of metabolism or oxidation meant no more than that the rate is one factor in the conditions which determine susceptibility. Child did not claim the conclusion was universally valid.4 Child allowed that in more highly differentiated organisms and in more advanced stages of development, the qualitative differences between organs may determine differences in susceptibility that are more or less specific.5

04

Use in development

The 1921 bibliography lists Child's paper on the gradient in susceptibility to cyanides in the ctenophore Mnemiopsis.6 The 1924 bibliography lists work on the axial gradient in the alga Griffithsia.7 In Physiological Foundations of Behavior (1924), Child called differential susceptibility a fundamental teratogenic factor wherever the whole embryo is exposed to an external condition, rather than injured mechanically in one part.8 Child described the modifications as non-specific and essentially quantitative in relation to the axes. Similar agents were said to produce the same sorts of modification in flatworms, echinoderms, annelids, fishes and amphibia.9

SourcesEach quotation was checked word for word against the passage it opens.
  1. the estimations of carbon-dioxide production lead to the same conclusions concerning the existence of metabolic gradients as do the results obtained by the susceptibility method.Child, C. M., 1915 · Individuality in Organisms · open at passage 112
  2. the demonstration of the metabolic gradients by means of the susceptibility method in Corymorpha, where most of the stem is naked, is not open to the objection which might be raised in the case of TubulariaChild, C. M., 1915 · Individuality in Organisms · open at passage 219
  3. the reagent penetrates the tissues only or chiefly from the cut end and so produces a death gradient which is merely a gradient of penetration and does not represent metabolic conditions.Child, C. M., 1915 · Individuality in Organisms · open at passage 219
  4. mean no more than that rate of metabolism or oxidation is a factor in the conditions which determine susceptibility, and it is not claimed that this conclusion is universally valid.Child, C. M., 1921 · The Origin and Development of the Nervous System · open at passage 73
  5. Undoubtedly, in the more highly differentiated organisms and in more advanced stages of development the qualitativeChild, C. M., 1921 · The Origin and Development of the Nervous System · open at passage 73
  6. The Gradient in Susceptibility to Cyanides in the Meridional Conducting Path of the Ctenophore, Mnemiopsis,Child, C. M., 1921 · The Origin and Development of the Nervous System · open at passage 433
  7. Experimental Alteration of the Axial Gradient in the Alga, Griffithsia bornetiana, Biol. Bull., XXXII.Child, C. M., 1924 · Physiological Foundations of Behavior · open at passage 787
  8. differential susceptibility appears to be a fundamental teratogenic factor in all cases where the modification results from exposure of the embryo as a whole to the external condition concernedChild, C. M., 1924 · Physiological Foundations of Behavior · open at passage 228
  9. It is perfectly evident that the types of developmental modification are non-specific and essentially quantitative both in their relations to the axesChild, C. M., 1924 · Physiological Foundations of Behavior · open at passage 228
Linked ideas
The metabolic gradients that Child demonstrated by susceptibility and carbon dioxide production are the axial gradients.
Child tied rate of metabolism or oxidation to the conditions that shape organismic pattern and development.
Regenerationrelated to
The Tubularia and Corymorpha argument concerns pieces cut from the stem and their physiological relations.
Susceptibility differences were treated as fundamental factors in organismic pattern.
Both treat differences in degree, not kind, as the basis of response to an external agent.
Polarityrelated to
Susceptibility ranking reveals a metabolic gradient along the hydroid axis (apical to basal), and differential inhibition can abolish original polarity, so the method probes polarity's gradient basis.
Both involve Planaria: passages say Child's first susceptibility-gradient observations used Planaria species. They say nothing about memory, so the link is shared organism, not shared mechanism.
Treats the susceptibility method itself; acclimation is the indirect form that reverses the apparent order of regions.
Where it is discussedPassages matching differential susceptibility, susceptibility to cyanide, susceptibility and rate of oxidation, susceptibility method
1924Physiological Foundations of Behavior · Child, C. M.27
1921The Origin and Development of the Nervous System · Child, C. M.12
1915Individuality in Organisms · Child, C. M.8