. \M1D0- ACIDS FORMED IN TKYPTIC DIGESTION. 42 1 
formula C 10 H 1: .\ <i . This substance gives a similar biuret reaction to that 
given by antipeptone^ like it also, it does not give .Mil Ion's reaction, is very- 
hygroscopic, and, on decomposition with hydrochloric acid, forms lysine and 
lysatinine, but not tyrosine. It has also been obtained directly from the pro- 
ducts of advanced tryptic digestion ; it has been found in milk, and in traces 
in the urine. It is easily soluble in water : sparingly in cold, more so in hot 
alcohol, from which it crystallises in microscopic crystals. It is also soluble in 
carbolic acid and glacial acetic acid, but is decomposed by these solvents, 
especially at a high temperature. It combines with hydrochloric acid and with 
phosphoric acid | Phospnorfleischsaure). The compound with phosphoric acid 
is the form in which it naturally occurs in the organism. Sjoqvist 1 has 
recently estimated the molecular weight of antipeptone by cryoscopic determina- 
tion at 250; this agrees very closely with the molecular weight similarly 
determined by Siegfried for his new acid, and increases the probability that 
the two substances are identical. 
When a proteid is subjected to tryptic digestion, a portion is decomposed 
beyond the stage of albumose or peptone, and there are formed several nitro- 
genous bodies of much simpler constitution ; of these, some are amido-acids 
and some organic bases. Of these substances, two amido-acids, leucine or amido- 
caproic acid, and tyrosine or para-oxyphenylamido-propionic acid, are present in 
much larger quantity than the others, which only occur in traces. These others 
are aspartic acid or amido-succinic acid, glutamic acid or amido-pyro tartaric 
acid, butalanine or amido- valerianic acid ; and of bases, ammonia, lysine, and 
lysatinine. Besides these substances of known composition, there is another 
substance of unknown composition formed, to which the name of tryptophan 
has been given, although it has never been isolated, and is only known through 
certain peculiar colour reactions which it gives. 
The amido-acids formed in tryptic digestion. 2 — Leucine — Leucine 
is an amidocaproic acid ((CH,) 2 CH.CH 2 .CH(XH 2 ).COOH), and is always formed 
in any profound decomposition of proteid, such as boiling with dilute acids or 
alkalies, fusing with alkalies, in tryptic digestion, or in putrefaction. It has 
been found in nearly all the tissues in the body, and there has been much 
discussion as to whether it is a normal constituent here, or is formed as a 
post-mortem product. Certainly it is rapidly increased in amount, because of 
proteid decomposition, after death, but the evidence is strong for its normal 
presence in more or less pronounced traces in most of the organs in the fresh 
condition. It is, besides, a very common constituent of tissue in many 
pathological conditions, and also occurs in the vegetable world. 
Yirchow showed that both leucine and tyrosine are found normally in the 
pancreas after death, and Kiihne afterwards showed that its amount here was 
much increased by auto-digestion of the gland tissue post-mortem. 
Leucine was first discovered by Proust in 1818 in putrefying cheese, and 
named by him cheese oxide (Kase-oxyd). It was also obtained byBraconnet 
by decomposing animal matter with sulphuric acid. 3 
Leucine may be prepared in many ways : by tryptic digestion of proteids, 
by boiling various forms of proteid with dilute acids or alkalies, with stannous 
chloride and hydrochloric acid, with bromine w 7 ater in sealed tubes, or by 
fusing with caustic alkalies. A common method is that of boiling horn 
shavings with dilute sulphuric acid for many hours ; but any form of proteid 
will yield it when so treated, such as meat, cheese, fibrin, wool, feathers, 
elastic tissue. 
Leucine has been obtained artificially by Limpricht, 4 by acting on isoval- 
1 Skandin. Arch. f. Physiol., Leipzig, 1896, Bd. v. S. 277. 
2 For a very full account of these bodies, see Gamgee, " Physiological Chemistry of the 
Animal Body," vol. ii. p. 231. 
3 Maly, Hermann's " Handbuch," Bd. v. (2), S. 207. 
4 Ann. de chim., Paris, 1854, tome xciv. p. 243. 
