PHYSIOLOGICAL BASIS OF PATTERN 29 



of animals, including all the chief phyla and many of 

 the smaller groups and nearly a hundred species of 

 algae among plants, that axial gradients in susceptibility 

 to the action of at least a wide range of external agents 

 exist. The agents used in these experiments include 

 cyanides, many anesthetics, such as alcohol, ether, 

 chloroform, chloretone, some of the urethanes, etc., 

 carbon dioxide, various acids, alkalies, neutral salts, 

 certain alkaloids, vital dyes and physical conditions, 

 such as extremes of temperature and the negative factor 

 lack of oxygen. 1 Potassium cyanide has been much 

 used in these experiments first because very low con- 

 centrations are effective and second because it has been 

 found by a large number of investigators to be a power- 

 ful inhibitor of protoplasmic oxidation and susceptibility 

 to cyanide may therefore be regarded as to some extent 

 a comparative measure or indicator of rate of oxidation 

 in the parts, organs, or individuals or a particular species. 2 



1 The data on susceptibility as determined by death and disintegra- 

 tion of cells or tissues, so far as they have been published, appear in the 

 following papers: algae (Child, 1916^, e, 19170, b, 1919^); Protozoa 

 (Child, 1914^; Hyman, 1917); coelenterates (Child, 1918, igigb; 

 Child and Hyman, 1919); ctenophores (Child, 191 ;c); Planaria (Child, 

 19120, 19130, b, igi4c,d, 19166, igigc,d}; echinoderm eggs and embryos 

 (Child, 19150, 19160); annelids (Child, 19170*; Hyman, 1916); Am- 

 phibia (Bellamy, 1919); miscellaneous (Child, 19140, igisc, pp. 50-62). 

 Further data on susceptibility gradients in Protozoa, ctenophores, 

 Hydrozoa, flatworms, echinoderms, annelids, fishes and Amphibia, and 

 the chick embryo are not yet published. 



2 There has been much discussion concerning the nature of the 

 action of cyanides on living protoplasm. Some authors have believed 

 that they act essentially as reducing agents and so retard or prevent 

 the metabolic oxidations. Others hold that they inactivate oxidizing 

 enzymes and still others that their action is primarily on the state of 

 the colloids. The literature of the subject has recently been discussed 



