Biological Reserves

“Life,” wrote McNair Wilson, “interested John Hunter to the exclusion of everything else, and he studied life as he had begun to see it—namely, as the supreme resistance to the blind forces which surrounded it and impinged upon it . . . Life, on this showing, was self protective.” This “supreme resistance” of life leads in health to longevity, in disease or after injury to survival; and therefore it is of peculiar interest to surgeons. It appears to depend on an urge for continuing life common to all tissues, and easily demonstrated for certain cells in the laboratory by examining the resistance offered by renal and hepatic cells to a sequence of injuries produced by chemicals (for example uranium nitrate and carbon tetrachloride). Tissues differ from one to another in the tenacity with which they cling to life, some giving up before others. This may be of importance in the practice of the future, as the population of this and other countries ages. According to the Government Actuary’s projection, provided the general mortality rate continues to decline and' the fertility rate remains about the same, between 1951 and 1979 the total population of this country may rise by 1 % to 52,250,000; the pensionable population may rise by 43% to 9,500,000, while the number of children may fall by about 4% to 10,500,000. Doctors (and incidentally hospital planners) will have to deal with and provide for more aged and ageing tissues and for fewer children; they will also be able to determine whether the tissues of children of the present generation, who are growing to be larger and who are maturing earlier than the children of 25 or 50 years ago, will in fact retain their “desire for life” to ages sufficient to project them into the pensionable


BIOLOGICAL RESERVES
"Life," wrote M cNair Wilson, " interested John H unter to the exclusion of everything else, and he studied life as he had begun to see it-namely, as the supreme resistance to the blind forces which surrounded it and impinged upon it . . . Life, on this showing, was self protective." This "supreme resist ance" of life leads in health to longevity, in disease or after injury to survival; and therefore it is of peculiar interest to surgeons. It appears to depend on an urge for continuing life common to all tissues, and easily demonstrated for certain cells in the laboratory by examining the resistance offered by renal and hepatic cells to a sequence of injuries produced by chemicals (for example uranium nitrate and carbon tetrachloride). Tissues differ from one to another in the tenacity with which they cling to life, some giving up before others. This may be of importance in the practice of the future, as the population of this and other countries ages. According to the Government A ctuary's projection, provided the general mortality rate continues to decline and' the fertility rate remains about the same, between 1951 and 1979 the total population of this country may rise by 1 % to 52,250,000; the pensionable population may rise by 43% to 9,500,000, while the number of children may fall by about 4% to 10,500,000. Doctors (and incidentally hospital planners) will have to deal with and pro vide for more aged and ageing tissues and for fewer children; they will also be able to determine whether the tissues of children of the present generation, who are growing to be larger and who are maturing earlier than the children of 25 or 50 years ago, will in fact retain their "desire for life" to ages sufficient to project them into the pensionable groups (males over 65, females over 60), a possibility at present unresolved. A t all levels of animal life, the desire for life expresses itself in the possession of three forms of biological reserve-self-defence, self-repair, and self-adjustment.
As I intend to deal particularly with selfadjustment, I shall deal with self-defence and self-repair only briefly.

Self-defence
There are, of course, two contributory factors to self-defence: the general response, which is an immunological one, and the local response, which can also be examined by histological methods. Both these aspects can be investigated in the laboratory, for the general pattern of response in laboratory animals resembles that in man. What does vary is the efficacy of defence against the various forms of noxious stimulus; physical, chemical and bacterial. The possibility of differences in efficacy is present not only between laboratory animals and man (though they are not uniformly present), but also between the various species of laboratory animals. And more importantly, there may be such differences between human races. Thus the resistance of the peritoneal cavity of the African to pyogenic organisms is greater than that of the European or the Asian. This is obviously the kind of difference which will become of increasing importance as world distances are reduced by better and faster means of communication. It is already of great importance in prognosis for those who practise in multiracial societies.

Self-Repair
T he capacity to repair injured tissues and to regenerate lost tissues appears early in anim al life; it is found in those anim als whose constituent ceils increase in num ber after they first becom e individual. The capacity may be the expression of a physiological process necessary to replace the wear and tear of use in such epiblastic structures as skin and hair, and such m esoblastic structures as the cells of the liver and the pancreas, and those of the blood. T he capacity may be extended to the replacem ent of tissues lost or interrupted, which is called healing. In lower anim als, for exam ple in the lizard, a com plex structure such as a tail m ay be replaced not only in bulk b u t also in anatom ical structure. H igher anim als do not possess this useful capacity. In m an the m ost com plex repair is the restoration of the epithelial lining of the gut, which includes the restoration of glands appropriate to the segm ent of gut involved.
R epair in the covering epithelium , the skin, includes the nails but not hair or glands. It is curious that the only other epiblastic structure which has the capacity for self repair is peripheral nerve, because (to take a m otor nerve as an example) it is merely the interm ediate link in the function of m ovem ent, and neither the initiator of m ovem ents (the brain) nor their effector (the muscles) has the capacity to regenerate. In some m esoblastic structures in lower verte brates (the liver of the dog for exam ple) regeneration in bulk quickly occurs after rem oval of large parts of the organ. The rem oval m ust of course leave behind enough parenchym a to sustain life, but it is curious th at the organ should at once set about rebuilding parenchym a far in excess of physiological needs.
T he capacity to regenerate com plex tissues decreases as the evolutionary scale is ascended; and finally includes-because of its survival value-only the replacem ent of com m only injured tissues. All other losses are replaced by connective tissue during the process of healing. I doubt the desirability of attem pting to modify so fundam ental a process, especially since departures from norm al tim ing in the process of self-repair often lead to instability of the repair.
All these varieties of self-repair-physiological, replacem ent in form and replacem ent in bulk-can be studied in the laboratory, for in higher anim als including m an the prim ary structures-bone, muscle, and nerve tissue-are the same. It is of interest to recall the possibilities of repair indicated by Sir Jam es Paget in his fam ous Lectures on Surgical Pathology (3rd edition, 1870).
1. In tissues form ed entirely by nutrient repetition-blood, epithelia. 2. In tissues of lowest organization, or lowest chem ical characterconnective tissue, bone. 3. T he tissues inserted into other tissues, connecting them with other structures-nerve fibres, blood vessels. This classification m ight well be used today.

Self-Adjustment
T he capacity for self-adjustm ent is most im portant for survival in the anim al kingdom , and particularly so in m an. It comprises two different kinds of adjustm ent. In the one, the patient " m akes do" with w hat he has after some disease or injury has deprived him of completeness in some physiological function. A n exam ple of this type of adjustm ent are the trick m ovem ents possible after paralysis of certain peripheral nerves, as when in paralysis of the radial nerve extension of the wrist is partly carried out by strongly flexing the fingers and so tightening the extensor tendons.
In the other type of adjustm ent structures a n d viscera have to undertake to function under conditions im posed by the surgeon, fo r exam ple after the tran sp lan tatio n of m uscles from the preaxial to the p ostaxial aspect of the forearm to relieve rad ia l palsy, or after anastom osis of the jejunum to the stom ach in the operation of gastroenterostom y. In m any of the operations of surgery the success and even the safety of the procedures depend on the capacity of the hum an body for self-adjustm ent. W onderfully efficacious as this capacity usually is, it m ay often be im proved, and its final a tta in m ent of m axim um com petence hastened, by the judicious use of all the social, m ental and physical auxiliaries which a re collectively called rehabilitation.
1. T h e sim plest form of self-adjustm ent is seen after th e destruction or rem oval of one of paired organs such as the kidney. T he rem aining organ, although containing am ple parenchym a for physiological needs, usually enlarges a little, as if to provide a little biological reserve. A djustm ent to the loss of single organs is not possible. Som etim es the loss is fatal if not artificially com pensated (pancreas); som etim es it gives rise to profound changes in function of the m ost com plex description (pituitary).
2. Som etim es adjustm ent is possible in virtue of the excess of parenchym a in an organ or tissue, over w hat is the m inim um physiological req u ire m ent. T he body adjusts itself a t once to the loss of five or six hundred cubic centim etres of blood, as donors who give blood for transfusion well know. Such structures as the liver and the thyroid are con structed on such generous lines as alm ost to give the im pression th a t they are prepared to lose portions from disease o r from injury; it is difficult to associate this with any evolutionary process. O n the other hand it seem s a little odd th at although other structures should have plenty of sp are parenchym a, so im p o rtan t a structure as the pituitary gland should have little or none, which leaves it very vulnerable to disease.
3. Instead of using excess of parenchym a for m aking adjustm ents, the body m ay utilise the fact th at there is overlapping of function betw een organs. T hus after rem oval of one cerebral hem isphere, not all cerebral control is lost over the con tralateral side of the body; which helps to com pensate for the lack of self-repair in the central nervous system . T h e stom ach m ay be com pletely rem oved by the operation of total gastrectom y, after which the intestinal juices are capable of com pleting the digestion of food. C om pensations such as these are not possible when there is no overlapping of function, as in the case of the pituitary or the pancreas, which are the only sources of their secretions.
4. O ne of the m ost im p o rtan t self-adjustm ents m ade by the body is to som e extent a norm al physiological process; the m aintenance of the constant com position of the body fluids-the milieu interieur of C laude B ernard. T his com position is altered by a great variety of causes, ranging from the m etabolic disturbances which follow injuries (including operations) to the com plex alterations seen when the alim entary tract is obstructed. T he rapidity and com pleteness with w hich th e body can m ake these adjustm ents is m uch reduced by other factors to deal with w hich no com pletely satisfactory bodily m echanism s seem to have been evolved; extrem e fatigue, extrem e m alnutrition, the presence of " stress." and in cases of trau m a the presence of gross infection.

5.
A vast num ber of adjustments can be m ade which are related to the conduits of the hum an body. The simplest division of these is into channels to which there is an alternative, and channels which are single.
A lternative channels can be subdivided again. There are those which are provided by nature, and which are already in existence, such as the anastom osing arteries, veins, and lymphatics which may form a collateral circulation when the main vessels are blocked by injury or disease. There are "relief" alternative channels the result of disease, as when an infected distended gall-bladder ruptures into the neighbouring duodenum ; the anastomoses formed by these internal f istulae are seldom completely satisfactory from an engineering point of view, because of awkward and abnorm al differences of pressure in the hollow structures so joined, and the lack of accurate union of their respective epithelial linings. Finally, there are those m ade by the surgeon, to which the body must accustom itself-such as gastro enterostomy, or the deviation of the flow of urine into the bowel. Arrangem ents such as the latter may be only "one-way" affairs, for while urine-to-colon is an adjustable arrangem ent, faeces-to-urinary bladder is not.
When there is no alternative to a given conduit, the problem s posed to the body differ. When the passage is a m ere tube without m uscular walls, such as the A queduct of Sylvius, then the body is powerless. W hen the conduit has m uscular walls, the body uses for the necessary adjustm ent the capacity of plain muscle to hypertrophy, to ensure that an obstruction in the conduit will be at least tem porarily over come. This useful property of plain muscle was first noted by John H unter; the possibility of hypertrophy is also present in cardiac muscle (to overcome vascular resistance) and in striated muscle (to increase capacity for work).
Tubes such as each ureter and the alimentary canal are not pro vided with alternative routes. But when they are totally obstructed the technical problems they present are different. The ureter is straight and has not excess length, so that the upper and lower ends cannot be brought together after a piece of it has been removed. On the other hand the alimentary tract is mobile, and excessively long, and the surgeon can m ake abnorm al junctions between its proxim al and distal parts, to which the body has been proved by trial to be capable of self-adjustment.
These three biological reserves-the capacity for self-defence, the capacity for self-repair and the capacity for self-adjustm ent are essential for the continuance of the hum an race. When the surgeon intervenes, it m ust be to provide a solution which has not been elaborated by the body itself in the process of evolution. A nd he must always be careful rather to aid the efforts of the body itself than to attem pt to substitute his own.