sulphur cannot be Mulder's Products of position of latine, and the decom investigations of Laskowski, Rüling, Verdeil, Wal- searches. Larger ther, and Fleitmann, that the amount of sulphur amount of present in the blood constituents is three times, in present. many cases four times, as great as the apparently well established analyses of the author of the proteine theory had indicated. It further appears, that Proteine a body, destitute of sulphur, and having the compo- obtained by sition of proteine, is not obtained by the methods methods. given by Mulder; that fibrine differs in composition from albumen; that the albumen of eggs contains not less, but more sulphur than the albumen of the blood, which sufficiently explains the disengagement of sulphuretted hydrogen in the experiments made with the former on artificial digestion. The study of the products, which caseine yields when acted on by concentrated hydrochloric acid, of which, as Bopp has found, Tyrosine and Leucine constitute the chief part, and the accurate determination of the products which the blood constituents, caseine, and gelatine, yield when oxidised, among which the most remarkable are oil of bitter almonds, butyric acid, aldehyde, butyric aldehyde, valerianic acid, valeronitrile, and valeracetonitrile, have opened up a new and fertile field of research intą, numberless relations of the food to the digestive process, and into the action of remedies in morbid conditions; discoveries of the most wonderful kind, which no one could have even imagined a few years ago; and the investigation which I now proceed to describe, will, I trust, contribute to excite the hopes of che caseine, ge the blood consti tuents. mists and of physiologists, and encourage them to direct their efforts, more than they have hitherto done, towards this department of science. Acid reaction of the juices of flesh. Opinions of SECTION II. On the Constituents of the Juices of Flesh. It has long been known that the flesh of newlykilled animals reddens blue litmus paper, while nothing certain is known as to the nature of the free acid which causes this reddening. Berzelius, in his detailed investigation of the juice of flesh, observes on this subject as follows:*_ "When the liquid" (obtained by pressure from the muscular substance) "out of which the albumen " and the colouring matter have been coagulated, is evaporated after filtration, it leaves a yellowish "brown extract, of which alcohol takes up the half or 66 66 more with a yellow colour. After the evaporation "of this solution there is left an extract-like mass, "mixed with crystals of common salt, which has a 66 strong acid reaction, and notwithstanding leaves "on incineration an ash containing an alkaline car"bonate, thus proving that the mass contained an 66 organic acid, partly free, partly combined with "alkali. If the alcoholic solution be mixed with a "solution of tartaric acid in alcohol, potash, soda, " and lime are deposited in the form of tartrates, and * Handbuch, vol. ix. p. 573. "there remains in the alcoholic solution, along with "tartaric and hydrochloric acids, a combustible acid dissolved. The solution is digested with finely"divided carbonate of lead, till lead is detected in "the liquid; it is then evaporated, the lead preci"pitated by sulphuretted hydrogen, the acid liquid boiled with animal charcoal and evaporated. It leaves a colourless, very acid syrup, possessing all "the characters of lactic acid, but still retaining a portion of extractive matter mixed with it." 66 This is essentially the amount of all that is known in regard to the nature of the free acid present in the muscles. In his researches on urine and on milk, Berzelius, by employing a similar process, obtained also strongly acid extractive substances, the properties and chemical relations of which he explained by the presence of lactic acid. acid pre sent? Whether these statements can at the present time Is lactic be regarded as proofs of the existence of lactic acid, that is, of the acid now called by that name, will be best seen from the opinions which Berzelius entertained concerning the nature of lactic acid, both at the time when his researches were made (1807), and subsequently (1823 and 1828). On the occasion of his report on Daniell's lampic acid, Berzelius observes,* "These researches render "it very probable that the lactic acid, which occurs so frequently in the animal kingdom, and which I * Jahresbericht, Jahrgang ii. p. 72. 66 Earlier and later views of Berzelius as to the nature of lactic acid in 1807, 1823, 1828, "have endeavoured to prove in a former work to "be different from acetic acid, is likewise nothing "more than a similar combination of acetic acid "with a peculiar animal substance, which accompa"nies it in its salts, is the cause of the differ"ences between these salts and the acetates, and "moreover prevents the volatilisation of the acid, 66 as long as the foreign matter is not destroyed. "A further inducement to adopt this opinion is "derived from the circumstance, that concentrated "lactic acid, when neutralised with caustic ammonia " and heated, yields distinctly vapours of acetate of ammonia, becoming acid at the same time." 66 66 In the seventh yearly volume of his Jahresbericht, Berzelius again observes, in considering Tiedemann and Gmelin's important researches on digestion, on the occasion of their mentioning acetate of potash as an ingredient of saliva (p. 200), They" (Tiedemann and Gmelin) " assume, on the authority of Fourcroy and Vauquelin, as well as of "their own experiments, and, as they say, of mine also, that lactic acid is only acetic acid, rendered impure by the presence of an animal matter. I have 66 66 66 66 66 certainly made experiments with the purpose of "resolving lactic acid into acetic acid and a foreign "substance; but I am not aware that I have ever "succeeded in doing so; and as long as we cannot "obtain acetic acid from it without destructive 66 distillation, or as long as lactic acid cannot be "formed from acetic acid and an animal substance, 66 so long it is best to retain the name of lactic acid; " for if lactic acid be a chemical compound of acetic "acid with an animal substance, which enters into "the composition of the salts, and deprives the acetic "acid of its volatility, it would be as inaccurate to "call these salts acetates, as to call the sulphovi"nates or nitroleucates sulphates or nitrates." The true lactic acid tained of nature of In his last investigation on this subject,* Berze- and 1832. lius describes some experiments, from which it might be concluded that lactic acid contains no acetic acid, and he terminates his researches with the following words:" Future investigations must be chiefly "directed to ascertain, whether that which has been "called lactic acid be a mixture of two acids, which "resemble each other, but yet yield different salts." From these passages it is evident, that, at the time when chemists began to reckon lactic acid among the ingredients of the fluid of the muscles, the properties of the acid now known by that name were almost entirely unknown: so much so that the acid discovered by Braconnot, which is formed in rice-water and in the juice of beet-root, was considered as a peculiar acid, till L. Gmelin proved it to be identical with the acid of sour milk, and C. Mitscherlich described his method of obtaining lactic acid from sour milk in a state of purity. It is plain that the assumption of the existence of lactic acid in the animal body, founded, forty years ago, on grounds so uncertain and variable, could no * Annalen der Pharmacie, vol. i. p. 1. 1832. only ascer late years. The former evidence of the pre sence of lac tic acid in the body is |