Structure of Smooth Muscle. 503 



ally small pieces were fixed, but they did not give as good results as 

 did the larger pieces. This was due to the fact that in small isolated 

 pieces of muscle the tension is removed and consequently the fibers 

 in contracting take an abnormal wavy or zigzag course or become 

 otherwise distorted. In every instance when placed in Zenker's 

 solution the larger pieces were perfectly fixed throughout. 



When relaxed muscle is placed into fixatives which act slowly the 

 chemical stimulus itself is often sufficient to produce very firm con- 

 traction waves. 



On opening the abdominal cavity so that the alimentary canal is 

 exposed to the air for even a short time, strong peristalses appear. 

 In the small intestine the waves usually involve only a small part of 

 the entire circumference of the tube. In the large intestine, however, 

 the tube may contract firmly throughout the whole diameter and is 

 easily fixed in this condition. On removing the intestine from a 

 recently killed animal and placing it in warm Einger's solution 

 (37° C.) contractions, similar to those caused by exposure to air, 

 though stronger, are set up. 



The large intestine of dog and cat was found to be one of the most 

 favorable places to obtain both contracted and resting smooth muscle. 

 When this portion of the alimentary canal is stimulated, at the point 

 where the stimulus is applied, it contracts very firmly throughout the 

 entire circumference. Areas between the point of stimulation are 

 just as markedly relaxed. Furthermore, it requires considerable 

 stimulus to start peristalsis and the tissue contracts very slowly. 

 Hence whole segments were removed and fixed with portions remain- 

 ing entirely relaxed, others firmly contracted. This was consequently 

 excellent material for a comparative study of resting and contracted 

 muscle. 



When tlie large infestinc of tho dog is filled with feces, the muscle 

 normally contracts in rings around the feces. At other points it 

 is relaxed. From such areas with no special stimulus entirely con- 

 tracted and entirely relaxed muscle was obtained. 



In the chicken the muscle of the alimentary canal is highly irritable 

 so that the slightest stiuuilus induces contraction. The fixative alone 

 is sufficient to produce strong peristaltic waves. Contracted muscle 

 from the stomach, small intestine and csecum was studied. 



