298 COLLOIDS IN BIOLOGY AND MEDICINE 



tion there occurs a change in the distribution of potassium. There is 

 thus associated with each contraction and return to rest a shifting 

 of potassium, a shifting of the swelling and a change in the surface 

 tension. We may leave undecided which phenomena are primary and 

 which are secondary. A. B. MACALLUM calls attention to the fact 

 that next to hydrogen, the potassium ion has a greater mobility than 

 any other cation, and attributes to this the rapidity of the change in 

 surface tension, and the rapid contractility of muscle. 



The efficiency of muscle depends to a marked extent upon its 

 content of water (see J. DEMOOR and PHILIPPSON *) and may be 

 influenced by extreme dehydration (shrinking). Such extreme 

 shrinking may be brought about by the introduction of concentrated 

 salt solutions or glycerin as well as of numerous poisons (especially 

 veratrin) (see SANTESSOW* and GREGOR*). Under these circum- 

 stances the muscle is shortened, as when it is very much fatigued, by 

 tetanic contractions. 



Likewise, by unsuitable nutrition, which results in a greatly 

 swollen state, the efficiency of the muscle may be depressed. 

 TSUBOI brought about such a swelling in rabbits which were fed 

 entirely on potatoes. The water content of their muscles was from 2 

 to 7 per cent higher than normal. Potatoes are especially rich in 

 potassium, and in this connection it is natural to think of the swelling 

 which potassium salts also cause in gelatin and fibrin, and of the 

 influence 6f the K ion on the depression of muscle irritability, dis- 

 covered by R. HOBER. 



[W. BTJRRIDGE associates the occurrence of fatigue phenomena with 

 the accumulation of K ions in muscle and in blood. Adrenin an- 

 tagonizes K salts. 



In their Croonian Lecture on " The Respiratory Process in Muscle 

 and the Nature of Muscular Motion/' W. M. FLETCHER and F. G. 

 HOPKINS come to the conclusion that lactic acid is not a toxic product 

 but an essential agent in the muscular contractions. Its free H ions 

 in the presence of colloidal fibrils cause an increase in tension in the 

 fiber, either by increasing the muscular tension along the longitudinal 

 surfaces or by the process of imbibition. They studied the effect of 

 oxygen on muscle and found that it not only delays the stiffening of 

 muscle but may altogether inhibit its onset. A muscle forced by 

 stimulation to stiffening may be recalled again by oxygen to its pre- 

 vious flaccidity. It was shown that immersion of a fatigued muscle 

 in oxygen restored the osmotic properties to those of resting muscle. 

 Fatigued muscle contains more lactic acid than resting muscle, and 

 a fatigued muscle, after resting in an oxygen atmosphere, subsequently 

 contained less lactic acid. A. V. HILL and PARNAS from studies of 

 heat production in contracting muscle conclude that the combustion 



