a red pigment on exposure to the sunlight. This substance is differently coloured by various reagents, among which may be mentioned ferric chloride, which stains it green or blue.

Hæmochromogen has been described in the medulla by MacMunn ; the bearing of this observation on the relation of the gland to Addison's disease has, however, been discussed already (p. 304).

With regard to the inorganic constituents, the high percentage of potassium phosphate is no doubt due to the large amount of nervous matter present.

An aqueous extract of the suprarenals is highly poisonous (Foa and Pellacani, 1883): this is due to the presence of the alkaloid neurine (Marino-Zuco '); that is what one would expect from the large amount of nervous matter present.

PANCREAS

This organ is alkaline in reaction during life, and rapidly becomes acid after death.

3

The solids are like those usually obtained from cellular organs; viz. proteids, extractives (guanine, xanthine,2 hypoxanthine, leucine, tyrosine,3 uric acid, lactic acid, inosite), and a small proportion of inorganic salts.

An extract of pancreas is an active digestive fluid, and has the same action as pancreatic juice. This subject will be considered fully in connection with digestion.

Extirpation of the pancreas causes glycosuria (see p. 663).

SALIVARY GLANDS

The cells of the submaxillary gland contain proteids of which the most abundant is a nucleo-albumin; they also contain mucin, which passes into the saliva (Hammarsten ). The sublingual is similar. The parotid cells contain no mucin. A small amount of mucin is, however, obtainable from the investing connective tissue. In myxoedema (p. 504) the parotid cells, however, undergo mucoid degeneration. An extract of the salivary glands exerts a similar diastatic power to that of saliva, as it contains ptyalin. The action of saliva will be fully considered in connection with digestion.

1 Gazzetta, xviii. 199; Chem. Soc. Journal, Abst. 1889, p. 290.

2 Scherer, Ann. Chem. Pharm, exii. 276.

3 Virchow, Frerichs, and Städeler, Hoppe-Seyler, Physiol. Chem. p. 260. These substances are present in the perfectly fresh organ, and are not the result of putrefaction, as in the spleen. Zeit. physiol. Chem, xii. 163.

KIDNEYS

This is another organ, rich in cells, with a supporting framework of -connective tissue, and one has for the most part merely to repeat what has been already said for such organs.

The cells are arranged to line large numbers of tubules; the relation of these to the blood-vessels, and other facts interesting from the point of view of secretion, will be dealt with in our consideration of the urine. Here we have merely to deal with the general chemical composition of the organ itself.

During life the reaction of the renal tissue is alkaline, after death it becomes rapidly acid. Its specific gravity averages 1050.

1

Gottwalt gives the following numbers relating to the amount of proteids and albuminoids, obtainable from kidneys freed from blood; six analyses were made :

The following extractives have been obtained by various observers : Xanthine, hypoxanthine, creatine, taurine, leucine, cystin, urea, uric acid, glycogen, and inosite.

The kidney also contains a small proportion of inorganic salts.

Pathological conditions. In cases of poisoning by alcohol or phosphorus, in septicemia, in various specific fevers, and in certain forms of Bright's disease, the renal cells undergo a fatty degeneration: this in its early stages produces what is called cloudy swelling.

In certain other forms of Bright's disease, the interstitial connective tissue may be more particularly affected, leading to its overgrowth. In this condition the amount of gelatin and mucin obtainable from the kidney is increased.

In gout, there is not only a hardened kidney, due to connectivetissue overgrowth, but deposits of urate of soda may also occur, both within and around the tubules (see p. 510).

The kidney may, like the liver and spleen, undergo waxy de

1 Gottwalt, Zeit. physiol. Chem. iv. 431.

2 I have found that the proteids present in the kidney are globulins, one of which coagulates at about 50°C., and the other at 70°-75°; there is also a nucleo-albumin which becomes viscous on mixing it with solutions of sodium chloride, as is the case with lymph-cells (see p. 260). See Proc. Physiol. Soc. 1890, p. vii.

generation. The following is an analysis of such a kidney by Lambling:-1

Albumin

Globulins

Other proteids.

Gelatin

Waxy substance

Per cent.

0.792

5-553

0.485

2.685

0.992

The method of analysis was the same as that adopted by Gottwalt. The waxy substance was isolated by the method of Friedreich and Kekule,2 and then purified by Kühne's 3 method by artificial digestion with gastric juice and subsequent treatment with baryta-water. There is a diminution in the percentage of proteids as compared with healthy kidneys; but the amount of waxy substance seems small considering the advanced state of degeneration revealed by the microscope. Lambling considers it possible that the swollen appearance may be in part due to the formation of a substance of the nature of the hyalins described by Krukenberg (see p. 486).

Many other morbid conditions, such as abscesses, new growths, &c., may attack the kidney, but have no special chemical interest. The contents of cysts in the kidney have been already described (p. 353).

LUNGS

The lung is composed of many tissues, and thus its chemical conThe tissues present are epithelium, stituents are also very numerous. connective tissue, elastic tissue, cartilage, and involuntary muscle. The constituents of the lung are, therefore, proteids, gelatin, mucin, elastin, chondrin. The extractives obtainable are lecithin, leucine, taurine (in oxen), uric acid, inosite. The embryonic lung is rich in glycogen; in the lung of the embryo sheep, it has been found in as large an amount as 50 per cent. of the dry solids; it is absent from the adult lung. Lastly there is a small percentage of inorganic salts, Small quantities chiefly alkaline phosphates and sodium chloride. of sulphates and of calcium, magnesium, silica, and iron, are also found. Pathological conditions. The black pigment present in the lungs of dwellers in smoky atmospheres consists principally of carbon. Calcareous concretions may occur in the lungs and other parts the respiratory tract. They have the same composition as similar concretions elsewhere, consisting of lime salts (especially the phosphate

Compt. rend. Soc. biol. (2), v. 51.
Virchow's Archiv, xvi. 58.

5 Maly's Jahresb. iii. 31.

of

and carbonate) mixed with small quantities of organic substances, like mucin and albumin.

In tubercle and phthisis generally, the chemical composition of the lung differs with the very various physical conditions that may be present, such as consolidation, fibroid overgrowth, softening, breaking down, calcification of tubercular deposit, &c. The term caseation as applied to a certain stage in the breaking down of a tubercle (which in origin is a mass of lymphoid tissue) is one derived from the cheesy appearance of the deposit; there is no proof that any substance of the nature of casein is formed. It appears to be a stage in the fatty degeneration of the cells.

The presence of the tubercle bacillus in cases of phthisis is constant. The very remarkable statement has been made by E. Freund,' that the tissues, blood, and pus of tuberculous patients contain cellulose, and apparently the amount of cellulose stated to be present is greater thair would be accounted for by the presence of cellulose in the cell-walls of the bacilli themselves.

In pneumonia, the alveoli become filled with proliferated cells, and lymph exuded from the blood-vessels; the lymph coagulates, and thus the lung tissue is solidified, producing the condition known as hepatisation. Budde 2 attributes the coagulation that occurs to the presence of a large excess of very active fibrin-ferment in the tissues in this disease. When speaking of the occurrence of intravascular coagulation (p. 305), the fact was mentioned that solution of the clot often takes place with great rapidity; a vessel that is hard to the touch like whip-cord, from the presence of a clot within it, may in a few hours become perfectly pervious. The same holds with regard to the lung in pneumonia. Every clinical observer is familar with the rapid re-solution that occurs in cases of recovery from pneumonia.

The functions of the lung in respiration (Chap. XIX), and the composition and variations in the sputa in different conditions (p. 447), have been already considered. (For Charcot's Crystals see pp. 303, 563.)

TESTIS

The observations that have been made on the testis, and its secretion, the semen, are mostly of a fragmentary nature. A large proportion of the chemical constituents of the organ is composed of proteids, or substances closely allied to proteids, of which the most

1 E. Freund, Wiener med. Jahrb. 1886, p. 335.

2 Budde, Ueber das Fibrinferment, Würzburg, 1889.

important is nuclein. In addition a large number of extractives, both nitrogenous and non-nitrogenous, have been found. The following is a brief résumé of the chief observations that have been made.

Sertoli found that a watery extract of the fresh organ had an alkaline reaction; Treskin 2 found it had an acid reaction. The acidity is probably due, however, as in so many organs, to the commencement of post-mortem changes of the nature of putrefaction, and this view of the case is supported by the fact that Treskin found leucine and tyrosine to be present.

The proteids present are serum-albumin and a globulin precipitable by saturation with sodium chloride (Sertoli). Nuclein is present in abundance.

The extractives present are leucine and tyrosine (probably produced by post-mortem changes), lecithin, cholesterin, and fat (Treskin); creatine (Schottin 3), inosite (Schottin, Külz1); and, in a case of diabetes, glycogen (Grohe "); adenine, xanthine, hypoxanthine, and guanine (Schindler 6).

The salts present appear to be chiefly chlorides of sodium and potassium (Treskin).

The greater number of the above observations have been made on the testes of the lower animals, bull, dog, &c.

Semen. This is the secretion of the testis, generally mixed with the secretion of the prostate. It is a whitish, viscid fluid, containing innumerable spermatozoa, which originate from the cells of the tubules of the testis.

While alive the tail of the spermatozoon exhibits lashing movements, akin to those of a cilium, by means of which locomotion is accomplished. This power is retained for hours, or even days, in the alkaline fluids of the body, but it is destroyed by weak acids, and by all strong reagents like alcohol, chloroform, strong alkalis, &c. The movement is stopped by cooling to 0° C., and also by a temperature over 53° C. The latter temperature appears to coagulate the protoplasm and quite kills the spermatozoon.

The chief chemical constituent of the spermatozoa is nuclein (Miescher); this forms an external coating to the head, and within it

Sertoli, Gazz. med. veterinaria, anno ii. Milano, 1872; Hoppe-Seyler's Physiol. Chem. p. 773.

2 Treskin, Pflüger's Archiv, v. 122.

Schottin, Hoppe-Seyler's Physiol. Chem. p. 773.

4 Kiilz, Sitzungsb. d. Gesellsch, zu Beförd. d. Naturwiss. zu Marburg, 1876, No. 4. Grohe, W. Kühne, Arch. f. pathol. Anat. xxxii.

Schindler, Zeit. physiol. Chem. xiii. 438.

Verhandl. d. naturforsch. Gesellsch. in Basel, vi. 138.