CHAP. IX.] THE CONTRACTILE TISSUES. 401 



to be in the intermediate preparatory organ as the consequence of 

 the preceding day's exertions, are perfected into urea and excreted. 

 Thus the urine receives not only the nitrogen corresponding to its 

 proper day ; but also some which should have formed part of muscle, 

 and have been excreted on the morrow. 



The nitrogenous constituents of the urine are not 

 muscular ^ ie on ty constituents which suffer change during mus- 



contraction cular exercise; but the non-nitrogenous elements have 

 on tne non- excited less attention and still remain an object for exact 

 nitrogenous research. Kliipfel found that the acidity of the urine 

 as est i m ated by titration with soda solution was some- 

 times increased and sometimes diminished during mus- 

 cular exercise, even when the food remained constant. The experi- 

 ments of Sawicki gave the same results, and disclosed also that the 

 acidity was influenced by the quality and quantity of food taken far 

 more markedly than by the circumstance of muscular exercise. On 

 the other hand, Pavy noticed that the acidity of the urine was 

 increased during severe exercise; and Janowski seems to have come 

 to a similar conclusion. Kliipfel has surmised that the diminution 

 of acidity which is sometimes observed after muscular exertion may 

 coincide with an abnormally large excretion of acid sweat; but no one 

 has yet established this 1 . In the experiments of both Flint 2 and 

 Pavy 3 the proportion of sulphuric acid and phosphoric acid excreted 

 during labour was greater than during rest; while that of sodium 

 chloride was less under the same circumstances. In Sawicki's experi- 

 ments, referred to above, the phosphoric acid suffered no constant 

 variation from rest to labour. 



THE CHEMICAL CHANGES OF LIVING MUSCLE WHEN AT KEST. 



Many of the chemical changes of normal resting muscle have been 

 already described or implied in the Section on Muscle in action. 

 The "respiration" of excised muscles and the preservation of irrita- 

 bility by means of oxygen, were among the earliest discoveries of 

 muscular chemistry, and have been stated at length in the account of 

 the researches of Humboldt, Georg Liebig, Valentin, Matteucci and 

 Hermann. The general nature of the material exchanges of muscles 

 which are still in the circulation, is indicated in the conversion of 

 arterial into venous blood by muscles at rest ; but a point of special 

 interest is this, that the blood flowing from muscles paralysed by 



1 Kliipfel, "Ueber die Aciditat des Harnes bei Kuhe u. bei Arbeit." Hoppe- 

 Seyler's Med. chem. Untersuch., iv. p. 412, Berlin, 1871. Pavy, Lancet, London, 1876, 

 Vol. ii. p. 888. Sawicki, " Sauregehalt der Harnmenge in Arbeit und Kube." Pfliiger's 

 Archiv, 1872, Vol. v. p. 285. Janowski, "Sauremenge des Harnes in Verbaltniss zur 

 Muskelarbeit." Dis. inaug., Moscow, 1876. (The original is in Kussian, it is ex- 

 tracted into Hofmann and Schwalbe's Jahresberichte, Vol. v. pt. ii. p. 274.) 



2 Flint, New York Medical Journal, June, 1871. 



3 Pavy, Lancet, London, 1876, Vol. n. p. 881. 



G. 26 



