HUMAN PHYSIOLOGY. 



181 



nance, but in found alm> to exist with regard to foreign nubntanoea 

 introduced into the blood, whether accidentally aa poisons or in- 

 ;illy aa curative agents ; aa, for inatanoe, the presence of 

 arsenic in the blood ia followed by an irritation of the moooua 

 membranes throughout the body, whilst lead ia taken up in aome 

 way ao that the extensor muscloa of the fore-arm aro affected, 

 ami that peculiar kind of paralysis known aa lead palsy ia pro- 

 duced. In the aamo way, certain organa or tissues have the 

 t appropriating medicinal substances introduced into 

 the general circulation. This process of absorption, which is 

 -t step of the more complex one of nutrition, may some- 

 timea be observed : particles are soon to pass from the circulation 

 into the tissues, and, in return, other particles pass back from 

 the tissues into the circulation. But hero we are aimply upon 

 the threshold of the subject ; our knowledge extends no further ; 

 we know not, nor can wo observe how it is, that from the samo 

 blood such a variety of textures aro formed, nor the many 

 modifications the crude elements of the blood must pass through 

 they are converted into bone, flesh, or skin. 



Performing, as is supposed, some office in connection with 

 the manufacture of the blood or its circulation, aro two glandular 

 bodies, the spleen and the thyroid body ; these are known as 

 ductless glands, as no duct has hitherto been discovered in con- 

 nection with them. The spleen, which is a bluish-red-looking 

 mass, of a brittle consistence, in the adult weighs about seven 

 ounces, but is sometimes enormously increased in size by disease, 

 especially after intermittent fever, when it receives the common 

 name of ague cake. It is situated in the abdomen, on the left 

 side, embracing the larger end of the stomach, ani in contact 

 with the tail of the pancreas. The thyroid body ia a gland 

 composed of three lobes, of a brownish-red colour, weighing 

 from two to throe ounces ; it is situated in the lower part of the 

 throat, resting upon the windpipe ; when diseased, it becomes 

 enormously enlarged, and constitutes the disease known as 

 goitre or Derbyshire neck. As to the function of either of these 

 bodies, little is certainly known, though the subject has received 

 the attention of many of the most eminent of physiologists. 

 With regard to the spleen, it has been observed that towards 

 the end of the digestive process it is considerably enlarged ; and, 

 consequently, it has been thought that in some way it influenced 

 the albuminous elements of the food, elaborating them so as to 

 fit them for reception into the blood. Another opinion is, that 

 the spleen is a destructive organ, that in it the worn-out cor- 

 puscles of the blood are disintegrated and broken up. Still less 

 is known of the function of the thyroid body ; but the purposes 

 either of them serve are apparently not absolutely essential to 

 life ; as the spleen has been removed entire from dogs, and in 

 some cases from men, without any apparent ill results following ; 

 and the structure of the thyroid gland is also occasionally de- 

 stroyed by disease, without any great disturbance of the health 

 of the individual. 



The blood, in addition to supplying the nutritive material 

 from which all the structures of the body are formed, acts as a 

 vehicle to carry out of the body the decaying matter from the 

 worn-out tissues, the retention of which in the system would be 

 prejudicial to the health, or even destructive of life. 



There are three chief agencies by which this process of purifi- 

 cation is effected the lungs, the skin, and the kidneys. Of the 

 first two we shall speak when we come to the subject of respira- 

 tion. The kidneys are probably the most purely excretory 

 organs of the body. They do not form any substance for future 

 use in the system ; their office is simply to separate from the 

 blood certain matters \vhich would be injurious to the health if 

 not removed. Some traces of these organs are found in even 

 very low types of animal life, and the higher the animal is 

 placed in the scale of creation the greater development and im- 

 portance do these organs assume. In the human subject they 

 are two in number, and are placed deeply in the abdomen, one 

 on each side of the vertebral column, extending from the eleventh 

 rib to the superior margin of the os innominatum ; their shape 

 ia well known, somewhat resembling the bean which has been 

 named after them ; they are usually inclosed in the centre of a 

 mass of fat, and are held in their position by the vessels which 

 pass to and from them. Each is about four inches in length, 

 two inches in breadth, and about one inch in thickness ; their 

 weight varies from four and a half to six ounces each. They are 

 glandular bodies, composed of an immense number of minute 

 tubes, which aro lined with secreting cells; those tubes converge 



and empty themselves into one canal or duet, called the ureter. 

 Ramifying amongst these tubes are the ultimata branches ~) 

 capillary network of the renal artery, which brings to the kidney 

 the blood loaded with effete material. This artery breaks np 

 and submit* the blood to the action of the secreting cells of the 

 kidney, much in the same way as the portal circulation is sub- 

 mitted to the bile-secreting cells of the liver. The tabes, the 

 branches of the artery, and veins are bound together by con- 

 nective tisane, and the whole organ is inclosed in a capsule of 

 the same material. At the centra of the kidney, whore there is 

 a kind of notch, the artery enters, and the vein and the duct 

 leave the kidney. The ducts called the ureters an membranous 

 tubes, of the size of a goose-quill, about sixteen or eighteen 

 inches long, which convey the secreted nri.ie into the bladder. 

 Owing to the huge size of the renal arteries and veins, the 

 transit of the blood through the kidneys is so rapid, that it is 

 probable that the whole of the blood in its torn is purified by 

 them. Some of the elements found in the urine exist aa such in 

 the blood, but other elements are formed by the chemical 

 agency of the secreting cells of the kidneys. 



Healthy urine is a clear limpid fluid, of a pale-yellow colour, 

 generally acid in reaction in man and all carnivorous Mim^l^ 

 but alkaline and turbid in the herbivorous ; its average specific 

 gravity is from 1015 to 1025 ; the average quantity accreted 

 during the twenty-four hours is from thirty to forty ounces ; 

 but this, as well as the specific gravity, depends very much 

 upon the quantity of fluid taken, and also upon the activity of 

 the skin. 



Chemically, the urine consists of water holding in solution 

 certain animal and saline matters ; it contains about 33 per cent, 

 of solid matter ; but its constitution is best shown by the fol- 

 lowing table, which exhibits the quantities contained in 1,000 

 parts of urine : 



Water 967 



Urea 14'2 



Uric Acid -468 



Colouring Matter ) 



Mucous and Animal Extractive Matter . ) 



rSoda 



Sulphates -< Potash 

 (Iiime 

 fSoda 



Phosphates < Magnesia 

 (_Ammouia 



rn-i 'a f Sodium 

 Chlorides \ ~ 



( Potassium 



Hippurate of Soda 

 Fluoride of Potassium 



Salts 



10-167 



8-135 



Silica 



traces. 

 1000-000 



The quantity of water varies according to the amount of fluid 

 drunk and exercise taken, and is strongly influenced by some 

 mental emotions; in some diseases it is diminished, and in 

 others enormously increased. 



The largest and most important solid constituent of the urine 

 is urea ; this forms nearly half of the whole solid matter, and is 

 the most important, as it is the chief substance by which the 

 nitrogen of the used-up tissues and unutilised food is removed 

 from the body ; and also because the failure to remove it, from 

 whatever cause it may arise, is followed by the most disastrous 

 consequences to the health of the sufferer; every function of 

 the body suffering, but the nervous eystem chiefly. Some of the 

 most common results of the presence of urea in the blood of 

 ursemic poisoning, as it ia called are convulsions, loss of con- 

 sciousness, and eventually paralysis of all nerve power, and 

 death, resulting from the stoppage of the respiratory move- 

 ments. In any disease, such as scarlet fever, in which the 

 excretory function of the skin is for a time in abeyance, a 

 greater amount of work is required to be done by the kidney ; 

 and it is this fact which renders any chill under such circum- 

 stances so dangerous; as in that case the work ia increased 

 still more, and ia often greater than the kidney ia able to per- 

 form ; so the waste products and superfluous fluid accumulate 

 in the circulation, and dropsy often supervene*. 



Uric acid ia another nitrogenous compound, and is derived 

 from the same sources as the urea, and serves, in a minor 

 degree, the same purpose. The salts of the urine form a iourth 

 of the solid ingredients : the sulphates are probably derived 

 from the decompoahg nitrogenous tissues ; the phosphates aio 



