THE PHYSIOLOGY OF HEALTH AND DISEASE. CHAPTER THE FIRST. INTRODUCTORY.-STRUCTURE AND FUNCTIONS OF THE STOMACH. OBVIOUS as are the distinctions between animals and plants, when we contemplate their higher groups, it is no easy thing to give a definition that will at once distinguish the one from the other throughout all organic nature. The aphorism of Linnæus, That minerals increase, vegetables increase and live, and animals increase, live, and feel will not help us much in distinguishing animals from plants. What is meant by feeling? If we define it as a movement resulting from stimulus, then the sensitive plant, and sunflower, and a hundred other plants possess it. If we define it as a movement connected with a nervous system, then the sponges, many zoophytes, and other animals, possess it not; for we can find in them no nervous system. Aristotle said that an animal differed from a plant in the possession of a mouth. Difficult as it may be to detect a mouth in some of the smaller organisms, it perhaps is the most available of all the definitions that have been given. It also indicates another fact, and that is, that an animal possesses a stomach. Plants have no stomach; they derive their nourishment from the air and soil in which they live, and are as animals turned inside out. (Fig. 1.) the animal kingdom. It is that to which all other parts of the animal are, as it were, subservient. Animals exist without nerves, bloodvessels, and muscles; but none exist without a stomach. The materials of which all other organs in the body are composed, are first prepared and elaborated in the stomach; and Man, with his great apparatus of organs for fulfilling the various conditions of his existence, is dependent, in common with the minutest animalcule, on his stomach for the various functions he performs. It is through the medium of the stomach that the blood is produced, that the coarse forms of external matter are reduced and refined, so as to become fitted to form part of his material frame. Hence the stomach is one of the most important organs in the human body; and the functions it performs are of a primary value, in relation to the other functions of the system. It must not, however, be supposed that the only distinction generally present between plants and animals is the possession of a stomach by the latter. This is a matter of structure; and when we come to function, we see that, although the end of the performance of certain functions in plants is the same as that of animals, the way in which the functions are performed is very different. The consideration of this difference between the means employed for the performance of functions in animals and plants, embraces a very interesting general relationship between these two king doms of nature. We find, in fact, that all the food that is taken into the stomach of the animal is elaborated in the system of the plant; that, although man and other animals partake of animal food, the substances which they thus take are derived from animals which feed upon plants. Not only do plants supply animals with food, but they are mainly fed by means of two substances carbonic acid gas and ammonia, which are thrown off by animal bodies, and which, if they remained in the atmosphere, would render it impure, and unfit for the existence of animals. this all; for we find that during the use of their food, animals are constantly taking up oxygen gas from the atmosphere, which, if it was not replenished, would be speedily reduced, so that the air we breathe would not support life. Oxygen gas is constantly Nor is [Vorticella citrina, an infusorial animalcule.a the mouth, b commencement of stomach, c e continuation of same, d f pouches or prolongation of stomach.] the term polygastric (many-stomached), which he has applied to them. Other observers, however, do not agree with Ehrenberg with regard to the nature of the vesicles in the interior of animalcules, which he calls stomachs. One thing is certain, that amongst these creatures we have very simple forms of digestive apparatus. The freshwater hydra (Fig. 3) is another creature belonging to a class of animals (Polypifera), higher in their organization generally than the polygastric animalcules, which exhibit a very simple form of stomach. As the nervous and other systems of the animal become complicated, and we ascend in the animal scale, we find the stomach assuming a more definite form, and ex tended into an intestinal tube. In the simple forms of creatures we have spoken of, there is no distinction between the bag of the stomach, and the parietes of the animal forming its body; but when we Fig. 3. [Hydra viridis, a species of fresh-water polype. -a the body containing a cavity (the stomach) in its interior, bb tentacula, whereby it lays hold of its prey.] ascend to the insects and shell-fish, we find it lying amongst a number of other organs. (Fig. 4.) The complication of the structure of the stomach becomes much greater when we pass from the lower forms of animals we have mentioned to those belonging to the highest classes, such as the fishes, reptiles, birds, and mammalia. In examining into the minute structure of the stomach of the various forms of animals, we find remarkable adaptations to the kind of food of which the animal partakes, and the circumstances in which it is placed. Thus, as a rule, it is found that vegetable food is more difficult to digest than animal food; and throughout the whole animal kingdom, the size of the stomach, and the length of the intestinal tube, are greater in herb-eating than flesh-eating animals. In creatures also that ruminate, a remarkable complication of the stomach alone is found, in order to carry on that function (Fig. 5). In ruminating animals the food, roughly cut by the teeth, is received into one cavity of the stomach, and passed into a second, in which it becomes soaked, and is thence passed into the mouth; where, being placed between the teeth of the animal, it is subjected to a second process of mastication, which is called rumination. It is then swallowed a second time, and passes into two other cavities in the compound stomach, before it is in a fit state to be taken up into the system. The stomach of carnivorous animals is a remarkable contrast to that of the ruminants. In these creatures, man lives best on vegetable food alone. The fact is, man is adapted for very wide limits with regard to food, and there is much evidence to prove, that a due admixture of diet, procured from both animals and plants, is best adapted for the Fiy. 4. [A vertical longitudinal section of the common lobster (Astacus marinus.)- a mandibles and palpi, b the stomach, ce intestinal prolongation of the same, d the outlet, e the heart, fghia system of great blood-vessels distributed to the posterior portion of the animal, k l m great bloodvessels distributed to the sternal or anterior aspect of the body, n n n lobes of the liver.] as the lion, tiger, &c., it assumes the simplest form, the flesh they eat requiring little preparation for digestion. The stomach of man stands truly between these two classes of herb-eating animals on the one hand, and flesh-eating on the other-thus indicating that he is intended for a mixed diet. We shall find, as we proceed further in considering the subject of the structure of the digestive organs in man, that there is nothing to encourage the notion that Fig. 5. [Stomach of the sheep.-a, first cavity of stomachi, or paunch, very large; b, second cavity, lying to the right of e, the gullet, and much smaller than the first; f, the third cavity, containing longitudinal folds of mucous membrane; c, the fourth cavity, intermediate in size between the first, and second, and third; g, the canal which conducts from the third cavity, for the passage of the food after it has undergone the process of rumination; h, the pylorus; d, the duodenum.] development of his frame, and the healthy performance of all the functions of his body. Before we examine the minute structure of the stomach, by means of which it performs its important functions, we will glance at some of the organs in man and the lower animals, which are necessary to the procuring and preparation of the food before it is passed into the stomach for digestion. Among the organs which are supplementary to the stomach, and employed in the act of procuring food, are those of prehension. In man this function is performed by the hand and arm more especially; but amongst the lower animals we find various substitutes for this very distinguishing feature of man's economy. Amongst the lowest creatures, as the animalcules, we find the mouth is surrounded with delicate moving hairs, called cilia, by means of which currents are produced in the water and the food thus brought to the mouth of the animalcule. In the polype-bearing animals we find the mouth surrounded by tentacles (Fig. 3), varying in number, size, and structure; the purpose of which is not only to assist in moving the animal, but to enable it to lay hold of its prey and carry it into its stomach. In the higher orders of polypes, these tentacles are covered with cilia, which give greatly increased power to these organs as agents of prehension. In the jelly-fishes we also find tentacles, which are used for grasping the prey of the animal. In the shell fishes (mollusca) we likewise meet with appendages round the mouth of the animal, by which food is grasped previous to its being introduced into the stomach, and these organs attain their fullest development in the cephalopodous class, which includes the nautilus, argonaut, and cuttlefish; here the tentacles are powerful and complicated organs, enabling their possessors to secure for food animals higher in organization than themselves. In the articulate animals, as the worms, insects, crabs, lobsters, and spiders, the hard external skeleton of the animal assumes various forms, to facilitate the taking of prey, and the conveying it to the mouth. The segments of the skeleton, forming the jaws, are furnished with additional organs for this purpose, and, in the nippers of the crabs and lobsters, we have a remarkable example of the adaptation of the fore-feet jaws are the only instruments. In the carnivora, however, the legs and paws of both fore and hind-feet are used in seizing and securing prey. In the monkies we find the nearest approach to the human hand, wanting however, in that wonderful completeness which is given by the opposable thumb: they use also the fore and hindfeet alike for the purpose of seizing and conveying food to their mouth. In some animals, an elongation of the upper lip serves the purposes of prehension, as in the giraffe, and in many of the deer tribe. An elongation of the nose is frequently likewise used for prehension amongst the pachyderms; and we cannot fail to observe that the tapir is a transition from the hog to the elephant, in which last the adaptation of this organ to the function of prehension in the form of its trunk is most perfect. Here we must stop for the present, and in the next chapter consider the Teeth, Salivary Glands, and some other preliminary parts of the Digestive Apparatus. BIOGRAPHICAL ENIGMA. to the need of the animal for holding | MOURN Scotland, mourn! for thy most polished powerful prey. From the Invertebrate we pass to the Vertebrate animals: and here we meet with son, Who, e're he came to manhood's years, had won Repute for thee, and for himself a fame, The classic tome, or with a patience stern the Fish using its mouth for this purpose. The mouth of the fish is supplied with teeth, but they are not used in the same way as the teeth of man, but as organs of prehension. It is by means of the teeth that the fish holds his prey when it is seized, previous to swallowing. In the carnivorous reptiles we find the same arrange- The problem dark or abstract theorem, Stripped the mock heroes of their tinsel glory. ment; and the dreaded teeth of the Croco-To him were ever an amusing theme; dile are not organs of mastication, but of prehension. In the Birds, the tooth of the fish and the crocodile is modified into a beak or bill, the object of which is to pick up food, previous to its being conveyed into the gizzard. Amongst some of the birds, especially the tribe to which the parrot belongs, the foot and claws are used as assistants to the bill in performing this office. In the Mammalia we find very curious adaptations of particular structures to this function. In most instances the teeth and Science, the law of Nature's smallest part, He learned to know; and Beauty teaching Art, Gave to his intellect refinement rare; Wisdom and wit were his beyond compare. THE NAME OF QUEEN. THERE was a law amongst the West Saxons which forbade the wife of their king to take the title of sovereign, or even to sit on a throne by her husband's side. It ordained that any king who should contravene this custom should be deprived of the rights of royalty, and his subjects be set free from their oaths of allegiance. History shows that this law was rigorously observed. Ethelwolf having sought to give a royal title to his wife, daughter of Charles the Bald, was deprived of the crown, and obliged to cede it to Ethelbald, his son by a former marriage. There is still in our language a remarkable trace of this ancient law:-We have no word which corresponds to the French "reine," to the German "Königin," or the Latin "regina;" none, in fact, which is the feminine of king. The wife of the king is called queen, which in fact signifies a companion, and is a generical word; for, in the origin of the language, it was commonly used for both men and women, with that signification. It was also long employed to designate the companions of the prince; in Latin denominated comites-in French, comtes. DETERMINATION. a willing with our whole strength and soul; a concentration of our thoughts-a fixed, invariable aim at one mark-an undeviating adherence to the path we have chosen. "I will be Marshal of France," said the Duke of Belleisle; and repeating daily as he paced his room with hasty strides“I will be Marshal of France," he made it his constant aim, and the marshal's staff was his guerdon. READING. MONTESQUIEU has said that reading is only idleness in disguise. It is so for those who read rather than meditate, who desire rather to know what others have said, than to take the pains of developing their own ideas-who love reading rather than books. A lady, who was in the habit of devouring every modern work, especially romances, said-"What matters it whether their tendency be injurious to me or not? it is enough for me that I am amused." Reading is a useless labour, if we know not how to reflect and to compare; if the good thought of a writer does not kindle our spirit, sharpen our intellect, purify our judgment. If we read books without consideration and without forming any judgment upon them, the ideas of others only weaken our own, and deprive our mind of all origiMEN, for the most part, do not succeed nality; if we do not oblige ourselves to in their endeavours because they do not per- give an account of our reading, it leaves severe with tenacity-because they do not no trace, and forms no treasury of wisdom will with a resolute mind. It is not in within our minds. We must not only heap ability they fail, but in that firm determi- up, but select; not gather all which offers nation that vigorous perseverance, which itself to our hand, but rather pluck those is the one virtue requisite for the perfection fruits alone which have reached maturity. of all other virtues. No great work, no It is in the moral as in the physical world,— lofty deed, can ever be expected from those that which nourishes us is not the quancold, undecided characters who will and tity which we swallow, but rather that will not-who never know what they de- which we digest. The seed does not spring sire. These bend before every blast-bow up, or grow, unless we both choose good before every opposing power - have no seed and cultivate the ground into which conviction-no conscience of their own it is to be cast. Who does not know that therefore no will. Then the pro- a man may be deeply read in learned lore, pitious opportunity is lost, and courage and yet be a fool? The clear-sighted fails. They inspire no confidence, gain no man must guess at futurity. History loses influence over others, have no control over half its value to those who only read in it events. But man can, in the course of life, that which is past--they must also read in it accomplish immense undertakings, if only that which is to come. Read," said Seneca, he possesses the lever of a strong, inflexible" not that thou mayest know more than will, to turn aside the obstacles which ob- others, but that thou mayest know better struct his path. Let it be clearly under- than others. It is not the study itself, but stood, however, what is meant by will: it is the fruit of study which we require to see." 66 |