8o 



SCIENCE. 



[Vol. XI. No. 263 



ment, the blood supplied to the tissues is not completely aerated, — 

 a condition remaining in all forms lower than the birds. Many 

 functions peculiar to the mammal, or, if not actually characteristic, 

 but indifferently developed in lower forms, are still less marked in 

 the mammalian embryo. If there be consciousness, it is of that ob- 

 scure kind existing only in forms of life low in the scale. Re- 

 flexes, indeed, there are in abundance, and probably much nervous 

 automatism ; but such limited action of the nervous system is pre- 

 cisely what distinguishes lower from higher groups of animals. 



Nor is the adaptation of the newly born mammal to its surround- 

 ings immediate. Throughout the first days of the life of the in- 

 fant, such adaptation is very imperfect, and in consequence many 

 children perish. Further, the resemblance of the infant to animals 

 of lower groups is shown in many directions, and especially in the 

 neuroses and psychoses. The study of infant psychology has of late 

 attracted much attention, and promises most instructive results. 



Turning from embryonic and infantile life to the opposite pole of 

 existence, old age, there is much that points in the direction of re- 

 version. It is not a matter of great importance whether we regard 

 this as physiological or pathological. Shakspeare's unrivalled 

 description of the epochs (biological and psychological) of human 

 life will occur to many readers. We must not, however, push the 

 resemblances between the infantile and senile stages too far. 

 There is sometimes a functional likeness which can scarcely be con- 

 sidered genuine physiological reversion, although it is a species of 

 functional reversion, for the consequences are the same. But in 

 general in both conditions there is an imperfect adaptation to the 

 environment. Moreover, in certain respects the old man reverts 

 rather to the functional condition of lower forms of Ufe than directly 

 to a previous stage in his own existence. Thus the imperfect ac- 

 tion of the respiratory, circulatory, cutaneous, and also of the 

 nervous system, by which the functions of the cerebrum and the 

 senses are weakened, are all either physiological or pathological 

 reversions, as we choose to regard the matter. But it is not on 

 such facts, however, that I would rely to estabUsh the principles of 

 this paper. 



In the various stages of slow or natural death, we have the 

 clearest evidence of physiological reversion in not one but many 

 different systems of the body. 



Normally expiration is largely passive, though possibly less so 

 than the text-books of physiology have represented ; but, as is well 

 known, in the dying man this phase, and indeed all phases, of the 

 respiratory act are in turn or contemporaneously modified : there 

 may be a diminution of one phase, and an exaggeration of 

 another, etc. In the frog and turtle both inspiration and expira- 

 tion are active : in such animals we recognize a function, moreover, 

 of the mouth and pharynx, in respiration, normally unknown in 

 man. Dr. Garland has, however, pointed out that in the tracheot- 

 omized dog, and, as he believes, in man under the same circum- 

 stances, and also in the moribund, a form of the throat respiration 

 supervenes. He has proved this experimentally in the tracheotomized 

 dog (Journal of Physiology, vol. ii.). In other words, there is a 

 resemblance to what exists normally in the frog. Garland recog- 

 nized this, though he has not spoken of it as a physiological rever- 

 sion. But apart from this minor reversion, it is plain that in 

 general the respiration of the dying bears a resemblance to that of 

 the groups with an active phase in both halves of the act. Further, 

 there is frequently a marked facial and laryngeal respiration, so 

 well seen in the normal breathing of such lower mammals as the 

 rabbit. 



Accompanying this alteration in the respiration, there is a great 

 change in the circulation. As I have shown, as the result of a 

 special study of the subject ('The Rhythm and Innervation of the 

 Heart of the S>&a.-T\iri\e.,' fournal of Anatomy and Physiology, vol. 

 xxi.), functional action ceases in the hearts of the cold-blooded 

 animals invariably in a certain order ; that is to say, the parts latest 

 developed phylogenetically, as the ventricles, are the first to cease 

 to act. The same applies to the mammal, and I have elsewhere 

 (' A Physiological Basis for an Improved Cardiac Pathology,' 

 Medical Record, Oct. 22, 1887) expressed the conviction that it is 

 fortunate for man that such is the case. It is difficult to see how 

 the ventricles could retain at once that sensitiveness and power to 

 adapt to the ceaseless and innumerable changes in the inner life 



of a mammal, and also the resistance so marked in the auricles 

 and the great veins at their junction with the right auricle, corre- 

 sponding to the sinus venosus of lower forms. Now, in the mori- 

 bund there may be only an occasional beat of the ventricles to 

 several of the other parts of the heart ; or the ventricles may pulsate 

 so feebly as to expel but little blood : hence the latter becomes 

 gradually more venous, with corresponding effects in the venous 

 channels, which become more prominent ; in the nutrition, lead- 

 ing to lowered temperature generally most pronounced in the 

 parts most distant from the heart; in gradual loss of all the func- 

 tions of the cerebrum ; finally, the only muscles that are function- 

 ally active are the respiratory, the sphincters, etc. In a word, the 

 dying human subject sinks functionally lower and lower in the 

 scale of animal life. There is physiological reversion of the widest 

 kind. This seems the most instructive aspect of the facts ; indeed, 

 I can see no other way in which a really philosophical significance ' 

 can be read into such phenomena. 



It may be readily perceived that in sleep itself there is a daily 

 reversion. Sleep not only reduces all human beings to the one 

 level, but it puts all mammals on the one plane. Now, it will be 

 seen, if we consider the nervous system, that the parts peculiar to 

 man, or most developed in man, are the very ones that for the time 

 being are as good as annihilated in sleep. Why should this be so ? 

 Why should this order be followed.' To say that the parts of the 

 nervous system remaining functionally active are those necessary to 

 maintain the vital functions, in reality throws no light on the ques- 

 tion unless we regard man as derived from lower forms, while the 

 whole becomes clear enough if we admit this. Much the same line 

 of argument applies to the reversions witnessed in hypnotism, 

 somnambulism, and allied phenomena. 



Hibernation is one of the most interesting examples of physio- 

 logical reversion to be found. We witness in the bat, though one 

 of the most active of animils, a return during hibernation to a con- 

 dition very much like that normally present in a cold-blooded animal 

 such as the turtle ; while the cold-blooded groups themselves pass 

 into a winter sleep allied to the quiescent state of plants or the 

 ' resting stage ' of the infusorians. Reversion alone — physiologi- 

 cal reversion — seems to explain such behavior. 



These general phenomena prepare us to understand certain 

 results following experiment, which, so far as I know, physiologists 

 have never explained satisfactorily. I shall take my illustration 

 chiefly from cases mentioned in the ordinary text-books, and es- 

 pecially from the magnificent work of Prof. M, Foster, as in that 

 we find subjects usually considered from different points of view. 



It has been pointed out that if the nerves supplying the posterior 

 pair of lymph hearts in the frog be divided, though their action 

 ceases for a time, it is eventually resumed ; that if the sino-auricu- 

 lar junction of the heart of the turtle be ligatured under favorable 

 circumstances, the action of the auricles and ventricle, tempora- 

 rily arrested, may be resumed. 



In general, if the sinus, or the sinus and auricles, be ligatured off 

 from the ventricle in a frog or turtle, and all the cardiac nerves be 

 divided (precluding the possibility of nervous stimuli reaching them 

 from distinct centres), these parts of the organ, I have observed, 

 will beat more forcibly against the unusual resistance than before. 

 It is stated, that, when the cervical sympathetic is divided, the 

 dilatation and cessation of rhythmic action of the arteries in the ear 

 of the normal rabbit, ensuing, are finally followed by a return to 

 the normal condition. 



The latter has been explained by the assumption of a local ner- 

 vous mechanism, which, though habitually influenced by the central 

 nervous system, suffices of itself when the connection with the 

 nerve-centres is severed ; but such local nerve-mechanism has 

 never been demonstrated anatomically. These and many similar 

 cases are explicable by physiological reversion. In lower forms,' 

 in which it is quite impossible to believe in a local nervous mechan- 

 ism at all, there is pulsation in vessels, etc., owing to the rhythmical 

 action of unstriped muscular fibre or of cardiac muscle. This func- 

 tion of the muscle is no' doubt under the control of the nerve- 

 centres in all the higher groups of animals ; and when it is exhibited 

 apart from such connection, we naturally seek for an explanation^ 



1 This subject is discussed in my paper on the * Causation of the Heart-Beat,' etc., 

 in the Canada Medical and Surgical Journal, January, 1887, 



