The cells also from the very beginning are the organs that make the animal heat necessary for life. Rubner[52] proved that the source of at least 90 per cent. of the animal heat in the body is a result of the chemical changes—oxidation—in the food ingested: the other 10 per cent. is caused by muscular contractions, the flow of blood, the friction of joints, and like motions. This oxidation is more active in young animals than in adults, and in each it is, of course, a cellular process.
Living matter contains hydrogen, oxygen, sulphur, chlorine, iodine, fluorine, nitrogen, phosphorus, carbon, silicon, potassium, sodium, calcium, magnesium, and iron. The removal of one of these elements causes the death of the body. They must be arranged in a definite, prescribed order to constitute cellular protoplasm, and any disarrangement of this order causes intoxication, disease, or death. Hydrogen is a constant product in the putrefaction of animal matter, of animal food, and is present in the intestinal tract. Oxygen is found dissolved in water and loosely combined in blood as oxyhemoglobin. All the elements, except fluorine, combine with oxygen, forming oxides, and the process is called oxidation. The production of heat and all vital motion depend on oxidation, decomposition of matter. In the nuclei of cells there is a so-called "oxygen-carrier," a nucleo-proteid, which contains iron, and this appears to be the chief oxidizing agent in the body. Chlorine, which in hydrochloric acid is essential to digestion, is ingested as chloride, and leaves the body chiefly through the urine and sweat. Iodine is a necessary part of the thyroid gland, an indispensable vital organ. Fluorine is found in all cells. Nitrogen goes into the body combined in proteids; and phosphorus, combined in the alkalies and alkaline earths of the foods. Carbon occurs in all cells and leaves them through the lungs as carbon dioxide.
The amount of energy set in action in the body in the decomposition of any food is equal to the energy that had been expended in the synthesis of that food from its organic elements, and the liberated energy set free in the body appears as heat, work, and nervous impulse. In a plant the chlorophyl and the sun's rays combine water and the carbon dioxide of the air into sugar and free oxygen. This sugar is changed in a plant into starch, cellulose, and fat, and also, when combined with some nitrogen, into proteid. An animal eats this plant, which contains starch, cellulose, fat, and proteid, and it either adds these ingredients to its own substance or oxidizes them so as to prevent the destruction of its own substance. These are the ends of all food. Broadly speaking, plants synthesize elements; animals analyze them, reduce them into simpler bodies.
Such processes, and those of the other elements of the body, which have to do with the changing constituents of the human organism, are all cellular processes—metabolism. Hence the chief organic act of the body is metabolic; the basic organ of man is the cell. Arms, legs, heart, brain, stomach, and similar organs are secondary, though some of the latter are essential for certain operations. Now, one cell is an organ amply sufficient for metabolism, for the chief organic act of the body; hence it is a fitting receptacle for a substantial form, a soul. Therefore there is no reason why the soul may not be present in the one-cell stage of the embryo; and since there is no reason why it should not be present, but many why it should, it is present.
Conklin says:[53] "The fertilized egg of a star-fish, or frog, or man is not a different individual from the adult form into which it develops, rather it is a star-fish, a frog, or a human being in the one-celled stage. This fertilized egg fuses with no other cells, it takes into itself no living substance, but manufactures its own protoplasm from food substances; it receives food and oxygen from without and it gives out carbonic acid and other waste products; it is sensitive to certain alterations in the environment, such as thermal, chemical, and electrical changes—it is, in short, a distinct living thing, an individuality. Under proper environmental conditions this fertilized egg-cell develops, step by step, without the addition of anything from the outside except food, water, oxygen, and such other raw materials as are necessary to the life of any adult animal, into the immensely complex body of a star-fish, a frog, or a man. At the same time, from the relatively simple reactions and activities of the fertilized egg there develop, step by step, without the addition of anything from without except raw materials and environmental stimuli, the multifarious activities, reactions, instincts, habits, and intelligence of the mature animal."
An objection to the opinion that the soul is in the embryo from the beginning is made from a consideration of the facts that there appears to be an aptitude for life in certain animal cells and tissues after removal from the original host, or after the death of the host; and, secondly, that in other separated tissues life is undoubtedly made evident under proper conditions. Some parts of the human body can be grafted upon another human body, and human sarcomatous cells have been made to grow in vitro. Hair often lengthens after the death of a person, if no embalming fluid has been injected. Dr. Alexis Carrel[54] substituted a piece of a popliteal artery, taken from an amputated human leg and kept in cold storage for twenty-four days, for a part of the aorta of a small bitch, and the dog lived for four years afterward and died in parturition. Magitot of Paris, in 1911, took a piece of the cornea from an extirpated human eye, and with it replaced a part of an opaque cornea on another man, and this second man could see through the new cornea. Surgeons now remove skin, bone, and other tissues from still-born infants and accident cases, preserve these, for weeks if necessary, in petrolate and Ringer's solution in cold storage, and then graft them on patients to repair lesions in skin, bone, cartilage, or other parts of the body.
If these separated tissues are alive, what is the origin and nature of the life? Again, if there is a low form of life in these separated tissues, remaining after the departure of the human soul, why could not such a low form of life precede in the embryo the advent of the human soul?
What is the nature of the "life" in the parasitic sarcomatous tissue which has been seen to proliferate for a short time in vitro? We do not know, nor is it relevant to the question. That there is life of any kind in the cold-storage graft of bone and skin is certainly not evident; rather every evidence points to the absence of all life. When taken out of cold storage, and the ordinary forces which corrupt a dead body are permitted to work, these grafts corrupt exactly as any part of a corpse does. That there is life of any kind in these grafts is a gratuitous assumption. In cold storage they are kept ready for assimilation into the body as food may be kept. Bone and skin grafting is merely a peculiar form of assimilation. Food taken into the body through the stomach and entrails is prepared in the body and assimilated into the substance of the bones or skin or other tissues; the graft is ready for assimilation without this preparation because it is already bone or skin.
The vital principle in a man, or in anything else, is at the end, when it normally issues, of the same nature as it was in the beginning. If it is at perfection a substantial primary form, it always was such—a substantial form cannot issue from an accidental form. If the substantial form is the form of the cells in the completed organism, it was such before that organism was perfected, unless it replaced a lower substantial form; but there is, we repeat, absolutely no need for such a secondary form at the beginning. If the cells of the embryo (not the infused germ-cells, which are not the embryo) had a forma corporeitatis, or cellularis, or whatever you wish to call it, the human soul when it did come would not confer primal existence, would not be a forma substantialis, but an accidental form. "In proof of which," says St. Thomas,[55] "we must consider that a substantial form differs from an accidental form in this, that an accidental form does not give being simply, but such or such being; as heat does not give being simply, but heated being. So when an accidental form comes in, a thing is not said to come into existence or to be generated, simply, but to become such or such an object, or to find itself in such or such a condition. So, also, when an accidental form disappears, a thing is not said to be destroyed simply, but only to a certain degree. A substantial form, however, gives being simply; and therefore by its advent a thing is said to be generated simply, and by its recession to be destroyed simply. If, therefore, it happened that any substantial form other than the intellectual soul preëxisted in matter, by which the subject of that soul would come into actual being, it would follow that the soul would not confer being simply, and therefore would not be a substantial form; also that the coming of the soul would not be a generation simply, but only secundum quid—all of which is evidently false." Again, St. Thomas says:[56] "Some tell us the vital acts that appear in the embryo are not from the soul, but from the soul of the mother, or from the primitive force in the semen. Both these statements are false."
An application of the opinion offered here—that is, that the human soul is infused at the instant of conception—to multiple and monstrous embryos offers no real difficulty. There are two kinds of human twins—those from two distinct ova and those from one ovum. Two ova may come from one or different ovaries, or even from one Graafian follicle, be fertilized at the same time and develop synchronously. If the ova are placed at some distance apart in the uterus, two placentas appear; if the ova are near each other the placentas may fuse, but their circulations do not. Each child will have its own fetal envelope.