CILIARY ACTIVITY 31 



Metazoa, Reference to the behaviour of leucocytes, phago- 

 cytes, etc., will be found in works on bacteriology and medical 

 aspects of physiology. Attention will here be confined to the 

 phenomena of amoeboid movement, as they can be studied in 

 free-living forms. For quantitative treatment of amoeboid 

 activity the only accessible criterion of the energy of movement 

 is the rate at which the animal progresses. This has been 

 studied in relation to changes in external conditions in a 

 recent series of investigations by Pantin (1923-1925). Marine 

 amoebae were used in these experiments. Two species 

 (referred to as type A and B) were used, both being of the 

 '' Umax " form which progresses by protrusion of a single 

 anterior pseudopodium, thus tending, in the absence of external 

 interference, to move in a straight line. If the conditions of 

 the medium were kept constant, Pantin found that the velocity 

 of an individual amoeba was constant to within 5 per cent, for 

 periods of as long as twenty- four hours, and if the conditions 

 are changed without irreversibly damaging the organism, the 

 original velocity is regained when the initial state of affairs 

 is restored. This velocity is readily observed by timing with 

 a stop-watch the period which is required for an amoeba to 

 traverse a given number of divisions of the micrometer scale 

 of the microscope ocular. 



By this method Pantin has described the relation of amoeboid 

 activity to osmotic pressure, temperature, and hydrogen ion 

 concentration of the external medium. The amoebae studied 

 were, like many other contractile mechanisms, very insensitive 

 to OH ions. On the other hand, amoeboid activity is reduced 

 with mineral acids to zero immediately on the acid side of 

 neutrality, to be precise at a pH. of 6' 8. As long as the 

 hydrogen ion concentration is kept at a level above pH. 4*0 

 the stoppage is reversible, movement recommencing when the 

 organisms are transferred to an alkaline medium. But below 

 this pH. limit cytolysis occurs. The velocity of progression 

 increases continuously up to pH. 9*6 ; and the velocity curves 

 for hydrochloric, sulphuric, butyric, lactic, and acetic acids 

 closely agree (Fig. 11). 



It has already been suggested that production of acid in the 



