Glycocholic Acid, CHNO, found in the bile of herbivora and man. It crystallizes in fine white, glistening needles. It exists as the glycocholate of soda in the bile. By boiling with weak acid, it yields glycin and cholic acid.

In the bile certain matters also exist to which the color is due, the principal being bilirubin in man and carnivora, and biliverdin in herbivora. They are probably derived from the coloring matter of the blood. They can be recognized by treating the solution with nitric acid which is colored with red fumes, when a play of colors is seen passing through stages of green, blue, violet, red and yellow.

Lecithin, CH,NPO,, is a complex nitrogenous fat found in most tissues and fluids of the body, particularly in the nerve tissues and yelk of egg. It is an interesting product of decomposition of the constituents of the brain, and is related in constitution to the neutral fats; it may be regarded as an acid glycerine ether. It is easily decomposed when heated with baryta water, splitting into glycerin-phosphoric acid, neurin, and barium stearate.

Another body called Cerebrin, not containing any phosphorus and of doubtful composition, can be obtained from brain substance, and is also found in nerve fibres and pus corpuscles. It is a light colorless powder which swells in water.

Protagon, C160H308N, PO35, is by some supposed to be the chief constituent of brain substance, and by others a mixture of the last two bodies.

154

Neurin (Cholin), CH1NO2, is an oily liquid only found in the body as a product of the decomposition of lecithin, but it has been obtained synthetically.

Cholesterin, CН1О + H2O, exists throughout the body where active tissue change is going on, particularly the nervous centres. It is a monatomic alcohol, and is the only one existing free in the body. It may be obtained from gall stones, some of which consist entirely of cholesterin. It may occasionally be found in a crystallized form in many of the fluids of the body but never

in the tears or urine, and only seems to be an effete product, nearly all that produced in the body being discharged with the effete portions of the bile. It may be recognized by the shape of the crystals formed from a solution in alcohol, which are rhombic plates, in which one corner is generally deficient.

EFFETE PRODUCTS.

These, as has been stated before, are generally the outcome of the active chemical changes necessary for the growth and vitality of the living protoplasm, and are for the most part soon eliminated by the excretory glands, so that but small quantities of them can be found in the active tissues where they are produced. Urea, CO(NH4)2, is the most important constituent of the urine of mammalia, but not of that of birds or reptiles. Traces of it may be found in the fluids and tissues of the body. It is readily soluble in water and alcohol, and forms crystals when its solution is concentrated. It decomposes when treated with some strong acids or alkalies, taking up water and yielding CO, and NH,; and with nitrous acid gives CO2+ N + 2(H2O). It was the first of the so-called "organic" compounds to be made artificially, being obtained by Wöhler in 1828 by mixing watery solutions of potassium cyanate and ammonium sulphate, evaporating to dryness and extracting with alcohol, or, in short, by heating ammonium cyanate, with which it is isomeric.

Ammonium Cyanate.

Urea.

NH.CNO = CO.NH,.NH,.

It can now be produced artificially in other ways.

It has also been considered a monamide of carbamic acid (CO.OH.NH), a molecule of hydroxyl being replaced by one of amidogen, NH2, thus-CO.NH2. NH2. In the presence of septic agencies, in a watery solution, urea takes up two molecules of water and is converted into ammonium carbonate—

=

CO(NH2)2 + 2H2O CO(ONH4)2.

The so-called alkaline fermentation of urine depends upon this change. The reader is referred to the Chapter on Excretions (XXII), where more complete information is given.

Kreatin, CH,N,O2, occurs in muscle and many other textures.

It may be converted into kreatinin by the action of acids by simple dehydration. It can also be split up into sarcosin and

urea.

Kreatinin, CH,N,O, is a dehydrated form of kreatin, which is a normal constituent of urine. In watery solutions it is slowly converted into kreatin.

Allantoin, C,H,N,Os, found in the allantoic fluid and the urine of the foetus and pregnant women. It is crystallizable, and is converted into urea and allantoic acid by oxidation.

Glycin (Glycocoll or Glycocine), C2H2(NH)O.OH, is regarded as amido-acetic acid. It does not occur free in the body, but enters into the composition of the bile acids and hippuric acid. It is soluble in water, and insoluble in cold alcohol and in ether. Leucin, CH10(NH2)O.OH, or amido-caproic acid, is found in the secretion of the pancreas and some other glands. It is one of the principal products of the decomposition of albuminous bodies, from which it can be obtained by boiling with sulphuric acid, in the form of peculiar rounded crystals.

Tyrosin, C,HNO,, though belonging to a distinct chemical series (aromatic), is only found in company with leucin in the decomposition of albuminous bodies, and normally in the pancreatic secretion. Its constitution is said to give warranty for the name oxy-phenyl-amido-propionic acid.

Taurin, C,H,NSO,, is a constituent of one of the bile acids, and is also found in muscle juice. It may be regarded as amidoethyl-sulphonic acid.

Uric Acid, CH,NO, (dibasic), is found in large quantities in the excrement of birds and reptiles, but in a small and variable quantity in the urine of man. Traces have been found in many tissues, in some of which quantities accumulate as the result of pathological processes (gout). It forms salts which are much less soluble in cold than in hot water, and make the common sediment in urine. The acid salts are less soluble than the neutral. The common test for uric acid consists of slowly evaporating the substance to dryness with a little nitric acid, and to the residue adding ammonia, when a bright purple color is produced (murexide test). Uric acid is supposed to be a step

in the production of urea, which is one of the results of its oxidation in the presence of acids, thus :

Uric Acid.

Alloxan.

Urea.

C,H,N,O, + H,0+0=CH,N,O, + CO(NH,),. Hippuric Acid, C,H,NO, occurs in considerable quantities in the urine of the horse and herbivora generally. It is found but very sparingly in man's urine, but it appears in large quantities after benzoic acid and some other medicaments have been taken. In constitution it is an amido-acetic acid in which one atom of the hydrogen is replaced by the radical benzoyl (C,H,O). In the body it is combined with bases, and is formed out of benzoic acid and glycin (amido-acetic acid), thus:

Glycin.

Benzoic Acid.

2

Water.

Hippuric Acid. C2H2(NH2)O.OH + C‚H ̧O2 = C2H(C,H2O)(NH2)O.OH +H„O. By heating or putrefaction it is resolved into these constituents. Indol, CH,N, is produced in the intestinal canal by the putrefactive changes brought about by septic agencies during pancreatic digestion. It gives an odor to the fæces and a red color with nitrous acid.

Indican, a peculiar substance sometimes found in the urine and sweat. With oxidizing agents it yields indigo blue. By this fact it is easily recognized. An equal volume of hydrochloric acid and a very small quantity of calcium hypochlorite (bleaching lime) is added, and the indigo which is formed can then be dissolved and separated by agitation with chloroform.

CLASS B.-NON-NITROGENOUS.

GROUP V.-CARBOHYDRATES.

Carbohydrates (general formula, CHO) are bodies in which the hydrogen and oxygen exist in the same proportion as in water, the carbon being variable. The following examples of this group are met with in the textures of the body:

-

Grape Sugar (Dextrose), CH12O6, occurs in minute quantities. in the blood, chyle and lymph. It forms crystals which readily dissolve in their own weight of water. The watery solution has a dextro-rotatory power on the ray of polarized light. When mixed with yeast, the fungus (Saccharomyces cerevisia) of the

yeast causes alcoholic fermentation of the sugar, whereby alcohol and carbon dioxide are formed.

Moderate heat (25° C.) aids the process, and cold below 5° C. checks it; an excess of either sugar or alcohol stops it.

The presence of casein or other proteid material, when decomposing, gives rise to lactic fermentation, producing first lactic acid, then butyric acid, carbon dioxide and hydrogen.

CH12O62C ̧H2O,C,H,O2 + 2CO2 + H.

8

Milk Sugar (Lactose), CHO + H2O, metameric with cane sugar (sucrose). It is the characteristic sugar found in milk. It is not so soluble as dextrose, and does not undergo direct alcoholic fermentation, but under the influence of certain organisms it readily gives rise to lactic acid by lactic fermentation in the same way as dextrose. (See page 102.)

Inosit, C6H12O6 + 2H2O, is an isomer of grape sugar, which is incapable of undergoing alcoholic fermentation. It is crystallizable, and easily soluble in water. It has no effect on the polarized ray. It is found in the muscles, and also in the lungs, spleen, liver and brain.

Glycogen, CH10O5, a body like dextrin, first found in the liver. It gives an opalescent solution in water, and is readily converted into dextrose by an amylolytic ferment, or weak acids. It has a strong dextro-rotatory power. It can be found in most rapidly growing tissues. (See Glycogenic Function of the Liver.)

GROUP VI.-FATS.

These bodies have the same elements in their composition, but the hydrogen and oxygen have variable proportions-not that of water. Fats are found in large masses in some tissues, and also as fine particles suspended in many of the fluids. The fat of adipose tissue in man is a mixture of olein, palmitin and stearin, which are spoken of as the neutral fats.

The first is liquid, and the last two solid at normal temperatures, and the varying consistence of the fat of different animals