Figs. 27-29. These diawings were all taken troni the same region of the 

 intestine of Necturus. One side of the intestine was firmly contracted, the 

 other was relaxed. Fig. 27 is from resting muscle — r. nu., resting nucleus; 

 f. mf., fine myofibrilltp; i. c, loose interstitial connective tissue. Fig. 28 is 

 from muscle beginning to contract. Two contraction w-aves cross the section. 

 The portions of the nuclei in the contraction nodes are contractetl, showing 

 distinct shortening, thickening and massing of the chromatin. The portions 

 in the iuternodal segments are still relaxed. The rearrangement of the 

 chromatin meshes during contraction is shown well in this preparation. Each 

 end of nucleus (a) is in a contraction node, so shows contraction phenomena, 

 the center lies in an iuternodal segment, so has the structure of a resting 

 nucleus. The condensation of the connective tissue at the contraction node 

 is shown — c. u., contraction node ; i. s., iuternodal segment ; i. c, interstitial 

 connective tissue. Fig. 29 is from a firm contraction wave. The nucleus 

 (c. nu.) is short and thick. The chromatin is arranged in loops or festoons 

 (ch. f.) at the two ends — i. c, interstitial connective tissue. Ammonia alcohol. 

 Van Gieson's stain, x 19v'-<». 



Fig. 30. A section of a portion of the longitudinal uuiscle coat of the 

 oesophagus of pig stained in Mallory's anllin-blue connective tissue stain. 

 The contraction nodes (c. n.) are stained orange and appear for the most 

 part homogeneous. The myofibril he in the iuternodal segments are stained 

 bright red (f. mf.). The massing of the blue stained collagenous fibers in 

 the contraction waves is well demonstrated (c. f.). In the region of the 

 iuternodal segiuents the collagenous fibers are in a loose meshwork. The 

 enlargement of the muscle fibers in the contraction wave is distinctly shown. 

 In this preparation the nuclei are not well differentiated. Zenker's fluid. 

 Mallory's auilin-blue connective tissue stain, x HOO. 



Fig. 31. Cross-section of a portion of a contraction w^ave and uucontracted 

 area from the oesophagus of pig. In the contraction waves the contraction 

 nodes (c. n.) appear homogeneous and are stained orange. The internodal 

 segments (i. s.) are of less diameter and show the cut ends of the myo- 

 fibrillse stained red. The nuclei in contraction nodes are larger in cross- 

 section than they are in the iuternodal segments. In the contraction wave 

 the connective tissue (c. f.) is much condensed. Zenker's fluid. Mallory's 

 anilin-blue connective tissue stain. X HOO. 



Fig. 32. Cross-section of muscle fibers from the contracted carotid of ox — 

 e. n., a contractiou node. It is stained orange, but at the same time shows 

 the cut ends of myofibrilhie — i. s., either iuternodal segments of a contracted 

 fiber or an uucontracted fiber. The red myofibril hie are seen throughout the 

 entire sarcoplasm — e. f., elastic fiber ; c. f., collagenous fibers. Zenker's fluid. 

 Mallory's anilin-blue connective tissue stain, x 1700. 



Fig. 33. Portion of a contracted muscle flber from the cai'otid of ox. 

 Around the nucleus is a wide contraction node (c. n.). The end of the 

 fiber is uncontracted (i. s.). The contraction node is stained orange. The 

 (Continued on next page.) 



