CHAP. IX.] THE CONTRACTILE TISSUES. 359 



Changes in the non-gaseous constituents of Muscle in the states of 

 Activity and Rigor. 



1. Change in Reaction and its causes. 



During The flesh of dead animals, however fresh in the 



rigor the ordinary sense of the word, has an acid reaction. 



iTaTbeeT 1011 Berze j iusl > who discovered this fact, concluded from his 

 neutral or experiments that it was due to the presence in muscle 

 alkaline be- of that acid which his countryman Scheele had separa- 

 ted from sour milk. The lactic acid of muscle was shewn, 

 by the subsequent researches of Engelhardt, Heintz and Strecker, 

 to differ from the common lactic acid produced by fermentation. 

 Liebig, who at first denied the presence of lactic acid in muscle, after- 

 wards based many ingenious hypotheses upon its supposed presence 

 in the muscular tissue during life. All these chemists, because 

 they had discovered lactic acid in the flesh of recently killed animals, 

 concluded that it must have been present during life ; for, at that 

 time, the conception had not yet been formed that when a tissue dies 

 processes set in which may give rise to new bodies products of the 

 decomposition. This conception was due to Du Bois-Reymond. In 

 his papers on the reaction of the muscular tissue, and the changes 

 which it undergoes at death 2 , he established the immense importance 

 of distinguishing between a tissue which is yet living, though it 

 may be separated from the living body of which it once formed a 

 part, and one which has ceased to manifest the phenomena which it 

 possessed during life. With the cessation of these phenomena and 

 in warm-blooded animals that cessation follows so soon upon somatic 

 death as to be almost coincident with it there is a change in physical 

 properties and chemical structure. Thus whilst muscle is alive and in 

 a physiological condition it possesses a neutral reaction ; so soon as 

 it dies the reaction becomes acid. This change takes place so rapidly 

 in warm-blooded animals as to render it almost impossible to ascertain 

 the normal reaction; in cold-blooded animals, in which the vitality 

 of the tissues continues long, the acidification goes on so slowly as to 

 permit of its careful study. 



It is impossible to over-estimate the importance of these, the first 

 researches which pointed to the subtle differences which may exist, even 

 from a chemical point of view, between living and dead tissues ; the 

 conception which guided them and which was securely based upon 

 them, immediately led one of Du Bois-Reymond's pupils, Kuhne, to 

 the discovery of the most important points in the chemistry of living 

 muscle ; and it has since then so influenced the progress of Physiology 

 that we can scarcely realize how much we owe to it. Our knowledge 

 of the changes which occur in secreting glands in various conditions 

 of functional activity ; of the variations in the objective characters of 



1 Berzelius, Lehrbuch der Chimie, tibersetzt von "Wohler, 4th ed. Vol. ix. p. 569. 

 Ann. d. Chem. u. Pharm. Vol. i. p. 1. 



2 Du Bois-Eeymond, " Ueber angeblich saure Keaction des Muskelfleiscb.es." Gesam- 

 melte Abhandlungen zur allgeineinen Muskcl- u. Nervenphysik. Leipzig, 1877. Vol. n. p. 3. 



