268 LOCOMOTORY AND PROTOPLASMIC MOVEMENTS 



spore which moves at a speed of 0-2 mm. per second appears to move 

 very rapidly under a magnification of 300 diameters, since in one second 

 it appears to cover a distance of 60 mm., although it actually only traverses 

 720 mm. in the course of an hour. Relatively to their size, however, these 

 motile organisms are very active, for they may travel two or three times 

 their length in a second, whereas a man while walking may cover about 

 the half of his length in a second, an express-train may travel about one- 

 third of its length in a second, and the earth moves through a space of 

 about -f^-ft of its diameter per second as it rotates around the sun 1 . 

 A swallow may, however, cover 100 times, and a bee more than 1,000 

 times its length in a second, but here the movement is in a less resistant 

 medium. Many active fishes may cover their own length or several 

 times their length in a second, so that the zoospore is in this respect 

 inferior as a locomotory organism. Owing to the small size and relatively 

 large surface of the zoospore, it needs a greater expenditure of energy 

 per unit mass to give it the same velocity as a larger organism 2 . Zoospores 

 may indeed drag with them adhering bodies greater than themselves. 



Such forms as Chlamydomonas and Euglena respond at first by 

 a negatively geotropic movement when exposed to increasing centrifugal 

 action, and are only overcome by its mechanical action when its intensity 

 is eight times that of gravity. It follows that these organisms are able to 

 lift about eight times their own weight in water 3 , and according to Jensen 

 Paramaecium may raise nine times its own weight. Owing to the small- 

 ness of the organism, however, about 600 would be required to raise one 

 milligram 4 . To do this the two cilia of Chlamydomonas or the single one 

 of Euglena must develop as much energy as the cilia of ciliated epithelium 5 . 

 The strength of these organisms, is, therefore, greater than that of a horse, 

 which is able to lift a load about its own weight, \\hereas an insect can 

 raise a load about sixty-seven times greater than its own weight 6 . In 

 any case it is only to be expected that the movements of cilia and of 



Biitschli, 1. c. ; and Bd. II, 143. On Bacteria see Lehmann, Centralbl. f. Bact., 1903, 2. Abth., 

 Bd. x, p. 545. 



1 Nageli, Beitrage zur wiss. Bot., iSSo, p. 30. 



3 Cf. Pfeffer, Studien zur Energetik, 1892, p. 255. 



3 Schwarz, Ber. d. hot. Ges., 1884, p. 60. 



* Jensen, Centralbl. f. Physiol., 1893, Bd. vn, p. 568. 



5 Cf. Engelmann in Hermann's Handbuch der Physiologic, Bd. I, p. 392. 



* See Jensen, 1. c. [These comparisons are without value, since in the one case the weight 

 lifted is in water, but in the other 'in air. The experiments on centrifugal action can only yield 

 accurate results when the relative densities of the Paramaecium and of the liquid are known. 

 A living Paramaecium is evidently not much denser than the liquid in which it lies, so that but little 

 more work is done when swimming upwards than when swimming downwards, and in any case the 

 actual lifting power is relatively trifling. A Paramaecium having a diameter of 0-2 mm. when 

 spherical would have a volume of ^\^ cub. mm., so that thirty living ones would be needed to lift 

 a mass of one cubic millimetre of inactive Paramaecia in water ; but the actual power of work cannot 

 be given.] 



