30 COMPARATIVE PHYSIOLOGY 



though intra vitrant staining with methylene blue shows that 

 the diffusion of oxygen back into the depleted tissues is rapid. 

 The conclusion seems justified that while the ciliary mechanism 

 is ultimately dependent on the presence of oxygen, oxygen is 

 not a necessary factor in the contractile process, but only for 

 the maintenance of the requisite conditions for prolonged 

 activity. In other words, oxygen would seem to be concerned 

 with the recovery process, as in muscle. When movement is 

 abolished by deprivation of calcium or increased osmotic 

 pressure of the medium, the amount of oxygen consumed is 

 not affected for a considerable period of time. 



By means of Barcroft's manometer it is also possible to 

 obtain light on the nature of the substance on which a supply 

 of chemical energy available for transformation into mechanical 

 energy depends. If the ultimate fate of the substance is to 

 be oxidised, the " respiratory quotient " or ratio of CO2 

 evolved to O2 consumed must be unity for carbohydrates, and 

 about 07 in the case of fats and proteins. Gray finds that the 

 respiratory quotient for ciliary activity is about 0'8, which 

 implies that the substance used in ciliary activity is not 

 exclusively or mainly of carbohydrate nature, a conclusion which 

 agrees with the failure of micro- chemical m^ethods to detect 

 glycogen in the cells. Since fats are not stored by the ciliated 

 epithelial cell, it would appear that the substance on whose 

 energy the contractile mechanism depends is of a protein 

 nature. 



To sum up, the mechanism of ciliary activity may be 

 analysed on the basis of Gray's experiments into three com- 

 ponents ; a reaction by which free energy is liberated from some 

 chemical reserve, sensitive to monovalent ions (especially the 

 hydrogen ion), a mechanism by which this free energy is 

 transformed into mechanical energy, presence of calcium and 

 a. certain osmotic pressure in the external medium being 

 essential to its efficient working ; and, finally, an oxidative 

 recovery process which is necessary only for sustained activity. 



Amoeboid Movement. — Amoeboid movement is the character- 

 istic means of progression in certain Protista (Rhizopoda, 

 Mycetozoa, etc.) and the wandering cells present in many 



