a man, a woman, a horse, sheep, or fish. Others pretend, that they have been able to identify the blood of frogs and fleas!" The first person who directed attention to this point was M. Barruel;1 who was of opinion that a knowledge of the fact might be important in a medicolegal relation, with the view of determining the source of spots of blood on linen for example; but even admitting the fact, as stated by MM. Barruel, Devergie, and others, it is obvious, that so much must depend upon the power of olfactory discrimination of the observer, that the evidence in any doubtful case could scarcely be deserving of much weight. Mr. Taylor, indeed, affirms, that there is probably not one individual among a thousand, whose sense of smell could be so acute as to allow him to state, with undeniable certainty, from what animal the unknown blood had really been taken.

Besides the causes before referred to, the quantity of perspiration is greatly augmented by running or violent exertion of any kind; especially if the temperature of the air be elevated. Warm fluids favour it greatly; hence their use, alone or combined with sudorifics, when this class of medicines is indicated. M. Magendie3 conceives, that being readily absorbed they are readily exhaled. This may be true; but the perspiration breaks out too rapidly to admit of this explanation. When ice-cold drinks are taken in hot weather, the cutaneous transpiration is instantaneously excited. The effect, consequently, must be produced by the refrigerant influence of the cold medium on the lining membrane of the stomach,-this influence, being propagated, by sympathy, to every part of the capillary system. The same explanation is applicable to warm drinks; but the hot exert a sympathetic effect on the skin. by virtue of their stimulant action on the mucous membrane.

With regard to the uses of the insensible transpiration, it has been supposed to preserve the surface supple, and thus favour the exercise of touch; and also, by undergoing evaporation, to aid in the refrigeration of the body. It is probable, however, that these are secondary uses under ordinary circumstances; and that the great office performed by it is to remove a certain quantity of fluid from the blood: hence it has been properly termed the cutaneous depuration. In this respect, it bears a striking analogy to the urine, which is the only other depuratory secretion, with the exception of the pulmonary transpiration, which we shall find essentially resembles the cutaneous. Being depuratory, it has been conceived, that any interruption to transpiration must be followed by serious consequences; accordingly most diseases have, from time to time, been ascribed to this cause. There is, however, so great a compensation existing between the urinary and cutaneous depurations, that if one be augmented, the other is decreased,―and conversely. Besides, it is well known, that disease is more apt to be induced by partial and irregular application of cold than by frigorific influences of a more general character. The Russian vapour-bath exemplifies this; the bather frequently passing with impunity from a temperature of 130° into cold water. The morbific effect-in these cases

1 Annales d'Hygiène, i. 267.

2 Médecine Légale, 2de édit., iii. 761, Paris, 1840.

3 Précis de Physiologie, 2de édit., ii. 455.

of fancied check given to perspiration-is derangement of the apparatus engaged in the important functions of nutrition, calorification, and secretion, and the extension of this derangement to every part of the organism.

As the sensible transpiration or sweat is probably only the insensible perspiration in increased quantity, with the addition of saline, and other matters that are not evaporable, its uses demand no special notice.

2. The Lachrymal Secretion.

The lachrymal apparatus, being a part of that accessory to vision, was described under another head (vol. i. p. 283).

2

The tears, as we meet with them, are not simply the secretion of the lachrymal gland, but of the conjunctiva, and occasionally of the caruncula lachrymalis and follicles of Meibomius. It has been presumed, too, by several modern ophthalmologists-by Wardrop, Rosas, Jüngken, for example that a portion of them-Rognetta' says the principal portion-consists of the aqueous humour, which passes through the cornea by endosmose; but although such endosmose may exist, it can assuredly furnish but little towards the composition of the tears. They have a saline taste; mix freely with water; and, owing to the presence of free soda, communicate a green tint to blue infusion of violets. Their chief salts are chloride of sodium, and phosphate of soda. According to M. Fourcroy and Vauquelin,3 the animal matter of the tears is mucus; but it is presumed, by some, to be albumen or an analogous principle-dacryolin. They found them to consist of water, mucus, chloride of sodium, soda, phosphate of lime and phosphate of soda. The following is the result of analyses by Professor Frerichs:1-

When tears are examined with the microscope, globules of mucus, and debris of the epidermis are seen in them.

This secretion is more influenced by the emotions than any other; and hence it is concerned in the expressions of lively joy or sorrow, especially the latter.

3. The Salivary Secretion.

The salivary apparatus has likewise engaged attention elsewhere. It consists of a parotid gland on each side, situate in front of the ear, and

Traité Philosophique et Clinique d'Ophthalmologie, p. 705, Paris, 1844.

Frerichs, Art. Thränensecretion in Wagner's Handwörterbuch der Physiologie, 19te Lieferung, s. 621, Braunschweig, 1848.

3 Journal de Physique, xxxix. 256.

4 Op. cit., s. 618.

behind the neck and ramus of the jaw; a submaxillary, beneath the body of the bone; a sublingual, situate immediately beneath the tongue;-and an intralingual or lingual, seated at the inferior surface of the tongue; -the parotids and submaxillary glands having each but one excretory duct, the sublingual several. The structure of the salivary glands in man greatly resembles that of the mammary glands. The marginal figure exhibits their structure in the sheep. All these glands pour their respective fluids into the mouth, where it collects, and becomes mixed with the exhalation of the mucous membrane of the mouth, and the secretion from its follicles. It is this mixed fluid that has generally been analyzed by the chemist. When collected without the action of sucking, it is of a specific gravity varying from 1.004 to 1.009; translucent; slightly opaque; very frothy; and ultimately deposits a nebulous sediment. Even with the purest saliva there are always found mixed a few epithelial cells, derived from the mucous lining of the mouth, or from the excretory ducts of the secreting glands. It usually contains free alkali: in rare cases, during meals, Professor Schultz,2 of Berlin, found it acid; and during fasting, it is occasionally neutral. Mitscher

Fig. 330.

lich, indeed, affirms, that it is acid. whilst fasting; but becomes alkaline during eating, the alkaline character disappearing, at times, with the first mouthful of food. The average amount of the secretion in the twentyfour hours does not probably exceed four ounces. According to Berzelius, its constituents are-water, 992-2; peculiar animal matter, 2.9; mucus, 1.4; chlorides of potassium and sodium, 1.7; lactate of soda, and animal matter, 0.9; soda, 0.2. Drs. Bostock and Thomas Thomson" think that the "mucus" of Berzelius resembles coagulated albumen in its properties. In the tartar of the teeth, which seems to be a sediment from the saliva, Berzelius found 79 parts of earthy phosphate; 12.5 of undecomposed mucus; 1 part of a matter peculiar to the saliva, and 7-8 of an animal matter soluble in chlorohydric acid. This animal matter, according to the microscopic experiments of M. Raspail," is composed of deciduous fragments from the mucous membrane of the cavity of

1 Vol. i. p. 516.

Lobules of the Parotid Gland, in the Embryo

of the Sheep, in a more advanced condition. (Müller.)

2 Hecker, Wissenschaftliche Annalen, B. ii. H. i. § 32, 1835.

3 Rullier and Raige-Delorme, art. Digestion, Dict. de Médecine, 2de édit., x. 300, Paris, 1835.

4 Medico Chirurgical Transactions, iii. 242.

5 Physiol., ed. cit., p. 487.

6 System of Chemistry, vol. iv.

7 Nouveau Système de Chimie Organique, p. 454.

the mouth; and he considers, that the saliva is nothing more than an

Fig. 331.

albuminous solution, mixed with different salts, that are capable of modifying more or less its solubility in water, and of shreds or layers of tissue. MM. Leuret and Lassaigne' analyzed pure saliva, obtained from an individual labouring under salivary fistula, and found it to contain,-water, mucus, traces of albumen, soda, chloride of potassium, chloride of sodium, carbonate and phosphate of lime:-and Messrs. Distribution of Capillaries around the Tiedemann and Gmelin affirm, and their analysis agrees pretty closely with that of Van Setten-that it has only one or two hundredths of solid matter, which are composed of a peculiar substance, called salivary matter or ptyalin, osmazome, mucus, perhaps albumen, a little fat containing phosphorus, and the insoluble salts-phosphate and carbonate of lime. Besides these, they detected the following soluble salts;-acetate, carbonate, phosphate, sulphate, sulphocyanate of potassa; and chloride of potassium. Treviranus thinks the saliva contains a peculiar acid, to which he gives the name Blausäure, probably combined with an alkali; but its chemical properties resemble the sulpho-cyanic acid so greatly, that according to Kastner' they may be taken for each other. As the result of numerous analyses, Dr. Wright gives the fol lowing constituents of healthy saliva;-water, 988.1; ptyalin, 1.8; fatty acid, 05; chlorides of sodium and potassium, 1.4; albumen with soda, 0.9; phosphate of lime, 0-6; albuminate of soda, 08; lactates of potassa and soda, 07; sulphocyanide of potassium, '09; soda, 05; mucus with ptyalin, 2.6.

Saliva has also been carefully analyzed by Enderlin," who concludes that, like the blood, it contains no lactate, carbonate, or acetate; but its alkaline reaction is owing to the tribasic phosphate of soda, which serves also as a solvent of the mucus and protein compounds. The analysis of the ashes obtained from a very large quantity afforded, in 100 parts:

Still more recently, human saliva has been analyzed by Jacubowitsch and found to be composed as follows:

1 Recherches, &c., sur la Digestion, p. 33, Paris, 1826.

2 Recherches, &c., sur la Digestion, par Jourdan, Paris, 1827.

3 De Salivâ ejusque Vi et Utilitate, Groning., 1837; cited in Brit. and For. Med. Rev., Jan., 1839, p. 236.

4 Biologie, Band. iv. § 330.

5 Ficinus, art. Speichel, in Pierer's Anat. Physiol. Real Wörterbuch, vii. 634, Altenb., 1827. 6 London Lancet, Mar., 1842. 7 Annalen der Chemie und Pharmacie, Marz, 1844. 8 De Saliva, Dissert. inaugur. Med. Univers. Dorpatens; cited by Scherer, in Canstatt und Eisenmann's Jahresbericht über die Forstchritte der Biologie im Jahre 1848, Erlang., 1849.

The salts consisted of phosphate of soda, 0.94; lime, 0.03; magnesia, 0-01; chlorides of potassium and sodium, 0.84.

Messrs. Tiedemann and Gmelin, and M. Donné,' found the saliva invariably alkaline, when the functions of the stomach were well executed. The last gentleman considered acidity of the stomach a diagnostic symptom of gastritis; and Dr. Robt. Thomson observed the acid reaction in all cases of inflammation of the mucous and serous membranes. With the view of testing these points, Mr. Laycock3 instituted numerous experiments, and tabulated the results of no less than 567 observations. His deductions do not accord with those of M. Donné. They are as follows:-1. The saliva may be acid without apparent disease of the stomach, and when the person is in good health. 2. It is alkaline during different degrees of gastric derangement, as indicated by the tongue. 3. It may be alkaline, acid and neutral, when the gastric phenomena are the same; and, consequently, acidity of the saliva is not a diagnostic mark of gastric derangement; and, lastly-in general it is alkaline in the morning, and acid in the evening. In a more recent work M. Donné1 accounts for the varying testimony of different observers in regard to the chemical reaction of the saliva, by the greater or less proportion of the mucus of the mouth contained in the specimens subjected to examination. In the normal state, he affirms, it is alkaline; but the mucus secreted by the mucous membrane of the mouth being acid, the mixed fluid, to which the name saliva is given, must necessarily vary according to the proportion of each.

When saliva is examined by the microscope, it presents, besides a considerable number of lamellæ of epithelium, globules in variable quantity, which, according to M. Mandl, proceed partly from the muciparous glands of the mouth, and partly from the salivary glands. They cannot, however, be distinguished from each other.

As the salivary secretion forms a part in the processes preparatory to stomachal digestion, its uses have been detailed in the first volume of this work, to which the reader is referred. The view of MM. Bernard and Barreswil, and of Mialhe, that the saliva contains an active principle, analogous in its physical and chemical characters to diastase, as well as its action on amylaceous substances, is there described.

A soft, whitish or yellowish matter, of greater or less thickness, is constantly deposited on the teeth, which, unless attention is paid, accumulates, and sometimes adheres to them with great force, constituting hard and dry concretions, known as already remarked-under the

1 Archives Générales, Mai & Juin, 1835; and Histoire Physiologique et Pathologique de la Salive, Paris, 1836. 2 Records of General Science, Dec., 1836.

3 Lond. Med. Gazette, Oct. 7, 1837. See, for a detailed account of the saliva, Dr. S.

Wright, op. cit.

4 Cours de Microscopie, p. 208, Paris, 1844.

• Manuel d'Anatomie Générale, p. 488, Paris, 1843.