VITAL PHENOMENA 165 



while swollen makes it anisotropic and if dried in this condition 

 it will remain so until swollen again. The muscle fiber is aniso- 

 tropic. Meigs (1908 b) has shown that there are no isotropic 

 discs, but merely, regions of less density or anisotropicity. Engel- 

 mann showed that the catgut would not contract on swelling 

 unless anisotropic. 



It has long been known that sarcolactic acid is produced by 

 an active muscle, and increases in proportion to fatigue in a 

 muscle in a nitrogen atmosphere. Fletcher and Hopkins (1907) 

 have recently reinvestigated this question. If oxygen is ad- 

 mitted to the fatigued muscle in nitrogen, the lactic acid dis- 

 appears, and C0 2 and heat are produced. Some suppose the 

 lactic acid to be the cause of the contraction. Death rigor has 

 been compared to a long continued contraction, and is accom- 

 panied by lactic acid production. Winterstein (1897) has shown 

 that an oxygen atmosphere may prevent the production of acid 

 and likewise the death rigor in a dead muscle. Death rigor is 

 apparently caused by a certain low concentration of acid, and 

 When the acid increases above this the rigor disappears (Von 

 Furth and Lenk, 191 1). This is in harmony with the observation 

 of Spiro and others that low concentrations of acid cause swell- 

 ing of hydrophile colloid gels, whereas higher concentrations do 

 not. Von Furth and Lenk (1911) have shown that the muscle 

 during death rigor and immediately before it, has a great power 

 of absorbing water, but losing this power and even shrinking 

 a little, due to loss of water, after the passing of the rigor. The 

 shrinking is apparently due to the excess of acid. At a low acid 

 concentration the muscle proteins swell, shrinking at a higher 

 concentration. 



McDougal (1908), Meigs (1908 a) and others have revived 

 Engelmann's swelling theory of muscular contraction, with the 

 substitution of osmotic pressure, as illustrated by the following 

 model. A rubber tube has a series of close fitting metal rings 

 slipped over it so that the distance between them is less than 

 the diameter of the tube. The tube is closed at one end and 

 water is pumped into the other. As the volume of the contained 

 water is thus increased the length of the tube is decreased. The 

 metal rings are supposed to take over the function of the Krauze's 

 membranes of the muscle fiber. Later Meigs (1910) returned 



