CILIA 



78 



CILIA 



semble cross-striations and may be con- 

 fusing. 



Metachromism is shown best by cili- 

 ated cells arranged in rows. The most 

 studied examples are the lateral cilia 

 of the mollusc gill, especially Mytilus 

 and Modiolus, because in these species 

 the gills are primitive and simple. The 

 location and shape of the cells are shown 

 in Modiolus (Lucas, A. M., J. Morph., 

 1931, 51, 147-193; and J. Morph., 1932, 

 53, 265-276). Atkins, D. (Quart. J. 

 Micr. Sci., 1938, 80, 331-344) has made 

 a comparative study of these cells for 

 many families and genera of lamelli- 

 branchs. Gray, J. (Proc. Roy. Soc, 

 B. 1930, 107, 313-332) observed that the 

 waves were a succession of spikes and 

 semicircles and with the stroboscope, 

 which caused them to appear to stand 

 still, he measured the relative time con- 

 sumed by the active and recovery 

 phases of the beat. The ratio was 

 about 1 to 5. A photographic set-up 

 for obtaining a permanent record of 

 coordination of lateral cilia has been 

 described in some detail by Lucas, A. 

 M. (J. Morph., 1932, 53, 243-263). 

 However by this method stroboscopic 

 effects of the movie camera shutter may 

 give false impressions of the rate of 

 wave propagation. 



The most commonly used material 

 for studies on ciliary activity is the 

 frog's pharyngeal membrane, yet it is 

 poorly adapted for practically all the 

 problems for which it has been used 

 as will appear later. Many earlier 

 workers set up recording devices by 

 which records of ciliary activity were 

 recorded on smoked kymograph drums; 

 the cilioscribe, devised by Dixon, W. 

 E., and Inchley, O. (J. Physiol., 1905, 

 32, 395-400) is a good example and still 

 has merit for classroom demonstration. 

 The apparatus consists of a vertical 

 spindle against which is gently pressed 

 the ciliated surface of a strip of frog 

 epithelium. The cilia cause the spindle 

 to rotate and this in turn moves a light 

 weight drum on which an interval timer 

 marks rate of movement. The chief 

 difficulty is the variable amount of 

 mucus which collects on the spindle 

 interferes with its smooth rotation. 



Many investigators have used the 

 ciliated epithelium of the frog's pharynx 

 as a delicate indicator to show the re- 

 sponse of living tissue to a wide variety 

 of chemical substances, therapeutic 

 compounds, and biological extracts, yet 

 it was not recognized until the work of 

 McDonald, J. R., Leisure, C. E., and 

 Lenneman, E. E. (Am. Acad. Ophthal. 

 and Oto-Laryng., 1928, 318-354) that 

 the cilia of the frog's pharynx are under 



definite nervous regulation. A few 

 years later Seo, A. (Jap. J. Med. Sc. 

 Ill Biophysics, 1931, 2, 47-75) estab- 

 lished clearly that cilia respond to 

 stimuli through the glossopharyngeal 

 nerves and that the motor fibers are 

 carried along the palatine nerves. 

 Methods which had been used thus 

 far involved placing fluids or particles 

 on the surface but two years later Lu- 

 cas, A. M. (Arch. Otblaryng., 1933, 

 18, 516-524) devised a method whereby 

 ciliary activity could be followed di- 

 rectly under very low powers of the 

 microscope focusing on the high-lights 

 reflected from the surface of the moving 

 ciliary waves. Application of this 

 method the same year to the frog 

 (Lucas, A. M., Proc. Soc. Exp. Biol, 

 and Med., 1933, 30, 501-506) demon- 

 strated conclusively that the cilia in 

 the frog's mouth are normally not ac- 

 tive and are completely at rest. They 

 become active when particles, no matter 

 how fine and light they may be, are 

 added to the surface; even the addition 

 of clear saline solutions has the same 

 effect. Thus, the normal baseline for 

 ciliary activity in the frog's pharynx 

 is zero instead of some positive value 

 derived by the use of foreign stimulating 

 agents. Recently Steward, W. C. (Am. 

 J. Physiol., 1948, 152, 1-5) although 

 recognizing these facts, sought to estab- 

 lish some arbitrary baseline values for 

 cilia which had been stimulated by discs 

 and weights placed on the mucous sur- 

 face. His experiments gave a mean 

 velocity of 0.75 mm/sec. but he found 

 that even very light stimuli on the 

 membrane, well removed from the route 

 covered by the test object, would in- 

 crease the velocity 142 to 415 per cent. 

 Lucas, A. M. (Am. J. Physiol., 1935, 

 112, 468-476) designed a moist chamber 

 in which threshold levels of the nerve- 

 cilia and nerve-muscle preparations 

 could be determined simultaneously. 

 He found that the threshold current 

 which would stimulate the cilia by way 

 of the palatine nerve was 15.4 times 

 stronger than that required to activate 

 the muscles of the toe. The behavior of 

 of excised mucous membrane is quite 

 similar to that found in vivo, the cilia 

 are normally quiescent and become ac- 

 tive only when stimulated. 



What is needed is a different biologi- 

 cal material for studies where chemicals 

 are to be tested in which the cilia beat 

 incessantly, as in the oviduct of birds. 

 This was one of the materials chosen 

 when ciliary studies were just beginning 

 (Purkinje and Valentin, Muller's Arch. 

 Anat. and Physiol., 1834, 1, 391-400). 

 They used macerated black pigments 



