cxxviii MUSCULAR TISSUE. 



As far as can be concluded from the observations and experiments that 

 have hitherto been made on the subject, the striated muscular tissue is not 

 regenerated in warm-blooded animals. It is true that, when a muscle is cut 

 across, or a portion removed, the breach will heal, but the loss of substance 

 is not repaired by new-formed muscular tissue. Striated muscular fibres 

 have been found in certain tumours of the ovary and testicle, but these 

 cases are altogether peculiar and abnormal. 



Chemical composition of muscle. Muscular tissue contains nearly 80 per 

 cent, of water, so that in being dried it loses about four-fifths of its weight. 

 The chief and characteristic constituent of the fibre is an albuminoid body. 

 This was at one time regarded as fibrin ; but, as it was afterwards shown to 

 be not identical with that substance, it was distinguished by the name of 

 syntonin ; the grounds of distinction being, that syntonin is soluble in very 

 dilute hydrochloric acid, and can be extracted from muscle by that solvent ; 

 also, that its solution is precipitated by neutral salts. More recently, the 

 subject has been investigated by Kuhne, who maintains that the albuminoid 

 matter of muscle exists in the fibres in a liquid form during life, but coagu- 

 lates after death, and thereby gives rise to the cadaveric rigidity which 

 then invades the muscles. When extracted from fresh and still irritable 

 frogs' muscles at a temperature of freezing, this substance, which Kuhne 

 names myosin, is liquid ; but if it be then exposed to the ordinary heat of 

 the atmosphere it partially coagulates, and the portion then remaining 

 liquid (the muscle-serum) when heated to 112 F., or less if it be strongly 

 acid, yields a further coagulum, which Kuhne considers peculiar to muscle ; 

 and finally, at 167, ordinary coagulated albumen. The primary coagulation 

 is hastened by the presence of blood, and possibly it may be due to the 

 mutual reaction of two albuminoids analogous in their operation to the 

 fibrinogen and fibrinoplastin (or globulin) of the blood (antea, p. xxxviii.). 

 The coagulum of myosin is soluble in strong solutions of neutral salts, and 

 accordingly it may thereby be dissolved out of dead and rigid muscles ; but 

 it loses this property if previously dissolved in dilute hydrochloric acid. 

 It then, in fact, agrees with the so-called syntonin, which Kiihne regards, 

 not as an original albuminoid of muscle, but as myosin altered by the 

 process of extraction. It has been suggested that the ready solution of 

 muscular fibre in dilute hydrochloric acid may be owing to the presence of 

 pepsine in minute quantity. 



Other organic compounds also exist in muscle, but in very small proportion 

 in comparison with the albuminoid matter. Most of them probably result 

 from the process of wear of the original muscular substance. Among 

 the most notable are, 1. Kreatin and Kreatinine, both of them nitro- 

 genized and crystalline, the former neutral, the latter (derived from it), 

 alkaline ; both are also found in the urine. 2. Sarkin or (Hypoxanthin ). 

 3. Non-nitrogenized substances, viz. : grape sugar ; inosit an unferment- 

 able sugar from the tissue of the heart ; glycogen, at least in embryos and 

 young animals. 4. Various organic acids, viz. , lactic, inosinic, butyric, acetic, 

 formic and uric. 5. Salts, in which potash predominates over soda, 

 magnesia over lime, and phosphoric acid over chlorine, muscle, in this 

 respect, resembling blood-corpuscles as contrasted with serum. Lastly, a 

 variable amount of fat may be extracted from muscle, and also gelatin ; 

 the latter no doubt from connective tissue ; for it must be remembered that 

 a piece of muscle subjected to analysis comprehends, along with the proper 

 muscular fibres, more or less of connective tissue, blood-vessels and nerves. 

 The account here given of the chemical constitution of muscle applies 



