STIMULI AND THEIR ACTIONS 



369 



by means of the attached leg- bones, and a thread, passing over a 

 wheel and attached to a small weight, be drawn through the pelvic 

 bone, to which the muscle is also attached, every movement of the 

 muscle can be observed in a signalling-lever, which is fastened to 

 the wheel (Fig. 161). If, now, a dish containing ammonium carbon- 

 ate be brought under the muscle, the latter is chemically stimulated 

 by the vapours of the ammonia, and performs contractions, which can 

 be shown clearly by the lever and can be traced upon a smoked 

 drum. Biedermann ('80) observed a very remarkable phenomenon 

 in the sartorius muscle when he let it hang in a temperature 

 of 3° — 10° C. in a solution of 5 grs. common salt, 2 grs. 

 alkaline sodium phosphate, and 

 0'5 grs. sodium carbonate in 

 one litre of water (Fig. 162). 

 The muscle then showed rhyth- 

 mic contractions, a phenomenon 

 that otherwise is never observed 

 in this muscle during life, and 

 suggests constantly the rhyth- 

 mic motion of cardiac muscle- 

 fibres. 



The chemical effects of 

 stimulation in contractile sub- 

 stances, thus far spoken of, 

 consist of contractions. But 

 certain chemical stimuli pro- 

 duce expansion. Such, e.g., are 

 food-stuffs, and especially oxy- 

 gen. These phenomena have 

 been discussed elsewhere.^ 

 They consist chiefly in the 

 fact that in an atmosphere 

 free of oxygen Amceha and 

 marine B/iizopoda cease the 

 formation of pseudopodia and 



undergo a diminution of ex- 

 es 



pansory processes, developing 



the latter again when new oxygen is introduced. Kiihne 

 (I. c.) has observed the sanae in Myxomycctes, in the reticulate 

 Plasmodia of Didymmm, which lives upon decaying leaves. 

 When he introduced a dried, and, therefore, completely motion- 

 less, piece of the plasmodium into a vessel filled with water 

 boiled and hence free of oxygen, which was shut off by mercury 

 from the air, it remained in complete rest. But as soon as a few 

 bubbles of oxygen were added to the Bidijmium, the latter began 

 to extend pseudopodia and to spread itself out in an arborescent 



1 Cf. p. 2S4. 



B B 



Fig. 160. — Vorticella. a, Extended; h, contracted 

 after chemical stimulation (the stalk-muscle 

 is not seen) ; c, a piece of the stalk-sheath 

 containing the muscle-fibre, strongly mag- 

 nified. 



