(Continued from p. 219.)
CHAPTER 4
Tissue Differentiation-Diversity in Unity
We have thus far been dwelling upon the essential unity of the organic life of the body, as seen in the basic protoplasm and cell organism from which it all is derived. We are now to pass to the well-nigh limitless varieties of this cell-life in the various tissues which eventually form the whole body.
From the original single cell is first developed an enormous number of cells which are arranged into a membrane called the Blastoderm, which is composed of three layers, called the ectoderm, mesoderm, and endoderm. From these three layers are derived the tissues forming the different organs and systems of the fully developed body, which are coordinated into the complete organism. As their names suggest, the ectoderm is the source of the tissues of the outer covering, the epidermis with its appendages, and of the inner covering of the extremities of the gastro-pulmonary tract. From it also are derived the tissues of the nervous system. From the mesoderm are derived the connective and muscular tissues, the tissues of the blood and lymph vessels, and other inner vital parts. The endoderm includes the remainder of the gastro-pulmonary tract.* *For a summary of the various tissues, the reader is referred to Kimber and Gray's Textbook of Anatomy and Physiology, chaps. III., etc. McMillan Company, New York.*
We have perhaps anticipated the spiritual meaning of this differentiation. Doubtless in the earliest stages of cell growth there are the characteristic differences which we noted, for instance, in the development of the spiritual features of 2 Pet. 1:5-8. The growth however is more gradual than would be manifest in the formation of each new cell. It is well to remember this, and not to expect a too rapid maturing of the features there dwelt upon. In divine things as well as in nature haste is not the rule. The husbandman has "long patience" (Jas. 5:7). It is not so much the time element, as the actual spiritual growth. Some features may be manifest almost immediately; they may appear in the form of prompt boldness as in Saul of Tarsus:"Straightway he preached Christ in the synagogues, that He is the Son of God" (Acts 9:20). A similar boldness may not appear in others until the stimulus of persecution brings it out (Phil. 1:14).We are here examining the elements of the spiritual life in their hidden or embryonic stage. "As thou knowest not what is the way of the spirit, nor how the bones do grow in the womb of her that is with child:even so thou knowest not the works of God who maketh all" (Eccl. 11:5). It must suffice to say that from the very first there are the potential differences of which we have spoken. God through the indwelling Spirit will manifest the features implanted from the beginning. Is it not significant that the triune character of the life is marked out in these three elements-which will have their sphere of service respectively in the outer, the inner and the even more inward departments of the spiritual life? Doubtless this triune constitution enters into the minute, as well as into the complete "spirit, soul and body" of man (1 Thess. 5:23).
We pass to the more general classification of the tissues as seen in the fully developed subject. With all their variations, these may be arranged under four general heads. These are:1. Connective Tissue. 2. Muscular Tissue. 3. Nerve Tissue. 4. Epithelial Tissue. Connective tissue, as its name suggests, serves to connect and support all the tissues of the body. It is all developed from the mesoderm, has few cells comparatively, but much intercellular substance, in a variety of arrangement. It is not originative, but passive under the action of other tissues.
Muscular tissue, about one half of the entire body, has to do with all voluntary and involuntary motions. It is of course in immediate connection with the skeleton and the nervous system.
Nerve tissue is the material for all the vast system which concerns the reception of impressions from the outside, and the putting into activity every portion of the body. It forms the brain, the immediate instrument of the man, and is therefore perhaps in a more complete way than any other department of the body a figure of spiritual truth.
Ephithelial tissue is derived from all three layers of the blastoderm, and is composed almost completely of cells with a minimum of intercellular substance. It may generally be described as protective. The various membranes or coverings of the body, both without and within, are of this tissue. It is devoid of blood vessels, being nourished by the absorption of lymph passing to the cells through minute spaces within the intercellular substance.
The spiritual significance of these four classes of tissue is quite manifest, even looking at their most general aspects.
Connective tissue has to do largely with the entire framework. It has fewest cells, and most intercellular substance, what we might almost call the foreign element in the body. But while thus largely composed of mineral salts, these are by no means separate from the body, but in vital union with it, through the complete vascular or circulatory system. It thus answers to the presence of objective truth, permeating the whole being. How formless and weak would the spiritual man be without the complete infiltration of revealed truth into every department of his being. When we remember that the skeleton or bony framework is largely connective tissue, we see at once its place and importance.
We may say that the doctrinal portions of the Epistles answer in good measure to this framework. "Hold fast the form (ύπoτύπωσιv, underlying framework) of sound words, which thou hast heard of me, in faith and love which is in Christ Jesus" (2 Tim. 1:13). Here the outline of revealed truth gives its shape to the whole man, while its identification with him is seen in the mutual vital activities of faith and love that are in Christ Jesus. Thus the objective truth is of profit, being "mixed with faith" (Heb.4:2).
It will easily be seen how the whole spiritual framework receives its form from the great doctrinal truths largely brought out in the Epistles to the Romans, Galatians, Ephesians and Colossians. If souls are not impregnated with these truths they will suffer from a spiritual rachitis, or rickets, markedly present in children whose nutrition has been deficient in lime salts. These who weakly oppose doctrinal teaching, and plead for sweetness and beauty of character little realize how they would be removing the very basis and framework of all spiritual beauty. In a different way from that hinted by the poet,
"Every face however full,
Padded round with flesh and fat,
Is but modeled on a skull."
What would the softest, tenderest, most regular features be, if they did not have the sturdy bone beneath them?
A mere glance at the salient doctrines of Ephesians will bear this out. In the first chapter, where the fulness of our spiritual blessings is unfolded, we have the great framework of God's election as the basis of our being "holy and without blame before Him in love." Sonship, with all its sweetness and joy of relationship, rests upon the framework of divine predestination, "according to the good pleasure of His will." Everything is wrought out by "Him who worketh all things after the counsel of His own will" (verses 5,11). Even the foretaste and pledge of the coming glory is by the presence and indwelling of God the Holy Spirit. "In whom after that ye believed ye were sealed with that Holy Spirit of promise" (ver. 13).
The same could be said of the Epistles to the Romans and the Galatians. The solemn truth of man's real condition, his guilt, corruption and helplessness, here form the basis of all genuine conviction of sin, with the corresponding truths of justification and deliverance. No matter how deep the sense of sin in the soul, its fullest expression and form will be gathered from the doctrine of sin as set forth in the words of Scripture. "There is no difference, for all have sinned and come short of the glory of God; being justified freely by His grace through the redemption that is in Christ Jesus" (Rom. 3:22-24); "The Scripture hath concluded all under sin, that the promise by faith of Jesus Christ might be given to them that believe" (Gal. 3:22); "When we were yet without strength, in due time Christ died for the ungodly" (Rom. 5:6). How powerless are all the soft tissues of feeling and experience to give the solid peace like that set forth in, "A man is justified by faith without the deeds of the law;" "To him that worketh not, but believeth on Him that justifieth the ungodly, his faith is counted for righteousness" (Rom. 4:5). The utter worthlessness of the flesh, and its setting aside are not learned merely or primarily from experience, but from such basic truths as, "What the law could not do in that it was weak through the flesh, God sending His own Son in the likeness of sinful flesh, and for sin condemned sin in the flesh" (Rom. 8:3); "Our old man is crucified with Him, that the body of sin might be destroyed (Καταργηθ, annulled, rendered inoperative), that henceforth we should not serve sin" (Rom. 6:6). "I through the law am dead (literally, died, in the death of Christ) to the law, that I might live unto God; I am crucified with Christ, nevertheless I live; yet not I, but Christ liveth hi me" (Gal. 2:19, 20).
These illustrations of spiritual connective tissue must suffice. They will be multiplied by the thoughtful reader, and thus serve to establish the soul more firmly upon the solid basis of the Word of God.
Space will scarcely permit more than a passing glance at the various groups of connective tissue. For the sake of some measure of completeness, we will mention them.
1. Embryonal tissue, as its name suggests, is the earliest of these groups, with a large proportion of soft, mucous tissue, in which there is a large amount of semifluid intercellular substance, with small bundles of white fibrils. We may call it the forerunner of other forms of tissue, and perhaps receives the intermixed mineral salts which later on form the more stable structure. How delicate and tender are the first elements of divine life imparted to the soul.
2. Areolar tissue, a soft filmy substance, a network of fibrous and elastic fibers. It forms a web-like binding and supporting material, connecting and insulating entire organs. It is universally distributed throughout the body, forming a medium of communication by effusion of foreign elements, as air, water, or pus beyond the point of original deposit.* *Kimber and Gray, pp. 25, 26.*
This tissue may be considered the advanced form of the previous one, also a delicate and elastic forerunner of the more rugged tissues, but always remaining to fill its own important place. It might answer to the more elementary truths which precede but ever have a place in the "form of sound words" of which we have spoken.
3. Adipose tissue is in one sense a form of areolar, and well nigh coextensive with it. It is characterized by the very large proportion of oil cells, in which the nucleus is crowded aside into a very minor place. It thus largely serves as a storehouse for reserves of heat and energy. It is found almost everywhere-under the skin, beneath. the serous membranes, around the internal organs, as the kidneys, filling up the furrows of the heart's surface, acting as cushions for the joints, and in the marrow of the long bones. Its usefulness is thus beyond question. Beside being a reserve store which can be returned to the blood and used in heat and energy, it serves as a covering or insulator preventing the too rapid loss of heat through the skin. It also fills out and supports delicate structures as the eye, and in general protects blood-vessels and nerves. That it adds, normally, grace and beauty to the form is also apparent.
We have already referred to some features of its spiritual significance. It is almost the synonym for spiritual prosperity. "They shall be fat and flourishing" (Ps. 92:14); "My bones waxed old;" "My moisture is turned into the drought of summer" (Ps. 32:3,4). Such scriptures show the opposites of the presence or absence of this element. Alas, many know what it is to say "My leanness!" Even our most blessed Lord, when He had offered "all the fat" upon the altar, said, "I may tell all my bones" (Ps. 22:17).
On the other hand, beyond all other tissue fat lends itself to undue multiplication. It thus becomes the synonym for self-indulgence and its accompanying sloth and love of ease. Eglon was a fat man, and even Eli in the sloth of age and feebleness developed similar conditions. May the Lord preserve us from pandering to a state which develops into such disgusting, repulsive and enervating features.
4. Fibrous tissue lies at the opposite extreme to the adipose. It forms the ligaments binding the bones together, the tendons or sinews to attach the muscles to the bones, or to each other, insulating and protecting the heart and kidneys, and forming membranes about the various muscles. This tissue is white, strong and tough, only sparingly supplied with blood-vessels. It serves as a most essential "joining" between the other tissues, as already indicated. Spiritually it answers to the combination of firmness and yieldingness which gives room to all true activity. It enables one to adopt himself to circumstances without conforming to them. Paul could thus become "all things to all men that I might by all means save some" (1 Cor. 9:19-22).
5. Elastic tissue is related to, but distinct from, the fibrous. Its function is suggested by its name, and it serves to act as an elastic cushion between the vertebrae, preventing jar; also in the walls of the blood vessels, especially of the arteries, permitting their dilation and contraction. It enters into the formation of the bronchial tubes, lung tissue and vocal cords and uniting also the cartilages of the larynx. Even the objective truths of Scripture, when assimilated into our spiritual framework are not mere hard, formal statements of truth, harsh and unyielding as the law, but instinct with the grace of Christ. This is specially marked in all proper intercourse with one another. It prevents the exacting, grinding making of legal demands, and yet keeps us firm and loyal to the truth. "Finally, be ye all of one mind, having compassion one of another, love as brethren, be pitiful, be courteous" (1 Pet. 3:8; see also vers. 7,9; ch. 4:8-10; ch. 5:3-5).
6. Reticular tissue serves as a meshwork of fibrous tissue forming the framework of adenoid or glandular tissue, in the spleen and bone marrow, in the mucous membrane of the gastro-intestinal tract, in the lungs, liver, kidneys, and other organs, forming a framework supporting the capillaries and gland cells. Some would class blood and lymph under these tissues, but they are not wholly derived from the cells in the same way. There is a close resemblance in all this to the framework of the inner spiritual organs, which serve as filters for things passing through our hearts and minds. When we come to the significance of these various organs this will be more apparent. At present, speaking merely of the framework of strong tissue, it is easy to see that in the delicate and careful process of judging actions and separating the precious from the vile, there must be strength and firmness as well as sensitiveness of touch. Thus conscience is most sensitive, and can be easily injured, yet it must be unflinching in its judgment of evil. "Holding faith and a good conscience" (1 Tim. 1:19).
7. Cartilage is of three kinds; Hyaline, which covers the ends of bones and forms rib cartilage, also the matrix in which bones are developed; while fibro cartilage, connecting bones together at points more rigidly than by joints; and yellow in the epiglottis, Eustachian tube and external ear. It maintains the shape but allows a certain measure of flexibility. Thus all cartilaginous tissues suggest the same truth of firmness and consistency without rigidity. "To whom we gave place by subjection, no not for an hour" (Gal. 2:5). But, "They gave to me and Barnabas the right hands of fellowship, that we should go unto the heathen, and they unto the circumcision" (ver. 9). In our corporate relationships it is of all importance that cartilaginous tissue does not become ossified. Brittleness is the forerunner of schism. May we be kept in the youthful vigor which yields self but ever preserves principle. S. R.
(To be continued, D. V.)