HUMAN PHYSIOLOGY. 



HUMAN PHYSIOLOGY. I. 



IN h'w poetical " Essay on Han " Pope lays down tho dogma 



Hint " tlu< (.roper htm!.. ' and true a* that 



is. that tho human miud aiid it attributes nhould form tho sub- 

 ject uf man's investigut no lew true that hi* physical 

 and it* vital functions are subject* worthy of man's 

 It scorns strange that amongst the multiplied 

 juts of modorn education Human Anatomy and Physiology 

 should h.ivi' t'. .UIH! no place; but it is a fact that in our ordinary 

 .-.li. ..! teaching tlioao most important subjects have been entirely 

 ignored, and there is in consequence a most wide-spread and 

 ...nu.l.-t.- ignorance of even their most elementary facts. In 

 tins and following papers it is intended to give an account 

 cf tin- anatomy (structure) and physiology (functions) of tho 

 human body, which, whilst devoid of technicalities and minute 

 .-hall yet show clearly tho situation, and indicate 



TO important organs. 



;-o it is possible to understand the principles of 



Physiology, t is necessary that a correct idea should 



iio human body and the various organs of 



it is composed, for it would bo absurd in the highest 



; , for example, to explain the function of rospi- 



,it first describing the structure of the lungs and 



other organs concerned in its performance. It will bo well 



: i lino the body as a whole, and try to understand 



omplex and wonderful mechanism, and after- 



<ler the various organs in connection with the 



-i's they fulfil in the human economy. Examining then 



tlh- human I'.'.ly. we shall find that, in accordance with that 



luo.ntly obtains in Nature, it may bo divided 



i:.to t' or systems: these are tho bony skeleton, or 



-m ; the fleshy portion, or muscular system ; and, 



lastly, that portion made up of the brain, spinal marrow, and 



nerve cords the nervous system. Each of these must now be 



considered in their turn. Wo will take first that which may bo 



termed the foundation of tho structure 



THK OSSEOUS SYSTEM. 



The zoologists place man in that great division of the animal 

 kingdom called Vertebrata, the chief characteristic of which is 

 that all the animals contained in it have an internal skeleton 

 or hard portion upon which the external soft parts are moulded. 

 This skeleton is composed of a varying number of pieces of 

 what we call bone. With tho external appearance of bone 

 every one is, of course, perfectly familiar ; it is hard, generally 

 smooth, and, when fresh, of a pinkish-white colour ; but if a 

 section of any bone be made it is at once seen that it is com- 

 posed of two differing parts one, the external, is dense and 

 compact like ivory ; the inner, on the other hand, is spongy, full 

 of small cells like a honeycomb, and is consequently called the 

 cancellous or spongy texture. It has been said that in all bones 

 both these structures are found, but the relative proportion of 

 each varies according to the duties the bone has to perform ; if 

 strength and firmness are needed, the compact tissue is largely 

 in excess ; but where little strength is wanted, and lightness is 

 essential, there is a thin external coating of compact tissue, and 

 the bulk of the bone is made up of the cancellous structure. 



Chemically, bone is a compound of animal and mineral ele- 

 ments : the latter, which in the adult form two-thirds of the 

 whole, are mainly salts of lime, principally the phosphate ; the 

 animal elements consist of albumen, gelatine, and fat. 



From its animal elements bone derives its toughness and 

 elasticity, whilst its hardness and solidity are furnished by its 

 mineral constituents. Either element may be taken away from 

 bone without destroying its original form ; thus if a bone is 

 carefully burned all tho animal constituents may be driven off, 

 or if a bone is soaked in dilute muriatic or nitric acid, the 

 mineral elements will be dissolved out, but in neither case will 

 the external shape of the bone be changed. The animal portion 

 of bone is that which is first formed, and in the early stages of 

 embryo life is the sole constituent, the mineral elements being 

 deposited in it. This fact explains why an injury which would 

 fracture the bone of an adult only causes a child's bone to bend. 

 Old bones, like dry sticks, snap readily; young bones, like green 

 and growing boughs, easily bend, but break with difficulty. 



The human skeleton is mado up of 254 distinct pieces of 

 bone, and for convenience of description may bo divided into 

 a central column, the spine or backbone: three cavities the 



head, the thorax or chest, and the pelvis or abdomen ; and 

 two pair* of extremities, the arms and the log*. 



Tho spine is a flexible column composed of twenty-four bones, 

 called vertebra), piled one on tho other ; anteriorly, it is solid, 

 to give support and strength to the body ; posteriorly, it is 

 hollowed out into a canal to receive the spinal cord, one of 

 tho three great divisions of the nervous system. The length of 

 tho spine in generally rather more than a third of the body, 

 and is divided into three regions: tbe cervical or neck (7 

 vertebras), the dorsal or back (12 vertebras), and tbe lumbar 

 or loins (5 Tcrtebnc) ; tho solid anterior part rests on the pelvis 

 below, supports the thorax in the centre, and the head above. 



Each vertebra is composed of two main parts; tho anterior, 

 a semi-circular mass of bone, mainly composed of canccllons 

 structure called the body, and posteriorly of two arches of bone, 

 which spring from the sides of the body, and unite to enclose a 

 hollow space the spinal canal. These arches support various 

 projections called processes : tho articular to called because 

 they articulate (form a joint) with the similar processes of 

 adjacent vertebrae the transverse, and the spinons. It is the 

 latter which are felt projecting when the hand is passed down 

 tho spine. These all, but especially the two latter, are bound 

 together by strong fibrous bands or ligament*, and also gire 

 attachment to the powerful muscles by which the spine is 

 moved in every direction. The main bond of union, however, 

 between tho vertebrae are thick plates of cartilage placed 

 between and exactly corresponding in shape to the bodies of 

 the vertebras ; these not only closely connect the bodies together, 

 but by their elasticity act as buffers to break tho force of 

 concussions coming from above and below. 



The two uppermost vertebrae differ from all tho others in 

 an important respect : the first which is firmly attached to 

 and e-i.pports the head, hence called the atlas has nearly the 

 whole of its body scooped out, leaving a small anterior canal ; 

 the missing piece is found attached to the upper surface of 

 the body of the second vertebrae, the axis, where it forms a 

 process jutting up into tho anterior canal of the atlas, and 

 forming the axis on which that bone revolves ; it is confined 

 to its proper position by a strong ligament, which divides 

 the two canals of the atlas. When the head is turned from 

 side to side, it is not the head turns on the spine, but the 

 atlas that is carried round tho pivot of the axis ; to prevent 

 this movement being excessive, which would risk displacement 

 of the bones, and cause sudden death from compression of 

 the spinal cord, strong check ligaments run from each side of 

 the pivot of the axis to the back of the skull. As each indi- 

 vidual vertebra is so firmly connected with its neighbour, if 

 two vertebras are separated from the rest and examined, the 

 amount of movement between them will bo found to be very 

 limited; but in the spine, as a whole, very great freedom of 

 motion in every direction is obtained. 



The next portion of the skeleton we have to consider is the 

 first of the cavities, the head, " the most strongly fortified part 

 of the skeleton, the very citadel as it were of life," contain- 

 ing as it does the brain, the seat of the highest intellectual 

 powers, and the centre and origin of the physical faculties. 



The head is firmly attached to tho first of the spinal verte- 

 brae, and is considered by anatomists to be a continuation of 

 the spinal column, formed of four vertebrae, modified for the 

 purposes they have to fulfil. It is composed of twenty-two 

 separate pieces of bone, eight of which form the skull or 

 cranium, and fourteen the face. The cranium is in shape an 

 egg-like dome, larger behind than before, and generally nearly, 

 though seldom, quite symmetrical. It varies in its proportionate 

 size according to the age, sex, and race of the individual; 

 thus it is larger in proportion in the child than in the adult, 

 in the male than in the female, and in the Caucasian or 

 European races than in either tho Ethiopian or Mongolian. 

 The texture and density of the bones also vary, the skulls of 

 barbarous nations being generally much harder, thicker, and 

 heavier than those of Europeans. 



The eight bones composing the skull are: the occipital, 

 a single curved flat bone, which forms the hinder portion of 

 the skull, and presents on its under surface two processes, 

 which articulate with the atlas and a large oval aperture cor- 

 responding in position to the spinal canal, and through which 

 the spinal cord is continued into the brain; the parietal, a 

 pair of irregularly quadrilateral-shaped bones, which join th* 



