Chapter 3

Among insects, some (_e.g._ grasshopper, cricket, ant, etc.) produce young in the ordinary way, by the union of the sexes; in other cases (_e.g._ flies and fleas) this union of the sexes results in the production of a _skolex_; while others have no parents, nor do they have congress--such are the ephemera, tipula, and the like. Aristotle discusses and rejects the theory that the male reproductive element is derived from every part of the body. He concludes that "instead of saying that it comes _from_ all parts of the body, we should say that it goes _to_ them. It is not the nutrient fluid, but that which is _left over_, which is secreted. Hence the larger animals have fewer young than the smaller, for by them the consumption of nutrient material will be larger and the secretion less. Another point to be noticed is, that the nutrient fluid is universally distributed through the body, but each secretion has its separate organ.... It is thus intelligible why children resemble their parents, since that which makes all the parts of the body, resembles that which is left over as secretion: thus the hand, or the face, or the whole animal pre-exists in the sperm, though in an undifferentiated state ({adioristos}); and what each of these is in actuality ({energeia}), such is the sperm in potentiality ({dynamei})."

In later times the two great rival theories put forward to account for the development of the embryo have been--

(_a_) The theory of Evolution, which makes the embryo pre-existent in the germ, and only rendered visible by the unfolding and expansion of its organs.

(_b_) The theory of Epigenesis, which makes the embryo arise, by a series of successive differentiations, from a simple homogeneous mass into a complex heterogeneous organism.

The above quotation will show how closely Aristotle held to the theory of Epigenesis; and in another place he says, "Not at once is the animal a man or a horse, for the end is last attained; and the specific form is the end of each development."

Spontaneous generation is nowadays rejected by science; but Aristotle went so far as to believe that insects, molluscs, and even eels, were spontaneously generated. It is, however, noteworthy, in view of modern investigations, that he looked upon _putrefying_ matter as the source of such development.

A chapter of this work is devoted to the consideration of the hereditary transmission of peculiarities from parent to offspring.

The fifth and last book contains inquiries into the cause of variation in the colour of the eyes and hair, the abundance of hair, the sleep of the embryo, sight and hearing, voice and the teeth.

Widely different opinions have been held from time to time of the value of Aristotle's biological labours. This philosopher's reputation has, perhaps, suffered most from those who have praised him most. The praise has often been of such an exaggerated character as to have become unmeaning, and to have carried with it the impression of insincerity on the part of the writer. Such are the laudations of Cuvier. To say as he does, "Alone, in fact, without predecessors, without having borrowed anything from the centuries which had gone before, since they had produced nothing enduring, the disciple of Plato discovered and demonstrated more truths and executed more scientific labours in a life of sixty-two years than twenty centuries after him were able to do," is of course to talk nonsense, for the method which Aristotle applied was that which Hippocrates had used so well before him; and it is evident to any one that both his predecessors and contemporaries are frequently laid under contribution by Aristotle, although the authority is rarely, if ever, stated by him unless he is about to refute the view put forward. Exaggerated praise of any author has a tendency to excite depreciation correspondingly unjust and untrue. It has been so in the case of this great man. In the endeavour to depose him from the impossible position to which his panegyrists had exalted him, his detractors have gone to any length. The principal charges brought against his biological work have been inaccuracy and hasty generalization. In support of the charge of inaccuracy, some of the extraordinary statements which are met with in his works are adduced. "These," Professor Huxley says, "are not so much to be called errors as stupidities." Some, however, of the inaccuracies alleged against Aristotle are fancied rather than real. Thus he is charged with having represented that the arteries contained nothing but air; that the aorta arose from the right ventricle; that the heart did not beat in any other animal but man; that reptiles had no blood, etc.; although in reality he made no one of these assertions. There remain, nevertheless, the gross misstatements referred to above, and which really do occur. Such, for instance, as that there is but a single bone in the neck of the lion; that there are more teeth in male than in female animals; that the mouth of the dolphin is placed on the under surface of the body; that the back of the skull is empty, etc. Although these absurdities undoubtedly occur in Aristotle's works, it by no means follows that he is responsible for them. Bearing in mind the curious history of the manuscripts of his treatises, we shall find it far more reasonable to conclude that such errors crept in during the process of correction and restoration, by men apparently ignorant of biology, than that (to take only one case) an observer who had distinguished the cetacea from fishes and had detected their hidden mammae, discovered their lungs, and recognized the distinct character of their bones, should have been so blind as to fancy that the mouth of these animals was on the under surface of the body.

That Aristotle made hasty generalizations is true; but it was unavoidable. Biology was in so early a stage that a theory had often of necessity to be founded on a very slight basis of facts. Yet, notwithstanding this drawback, so great was the sagacity of this philosopher, that many of his generalizations, which he himself probably looked upon as temporary, have held their ground for twenty centuries, or, having been lost sight of, have been discovered and put forward as original by modern biologists. Thus "the advantage of physiological division of labour was first set forth," says Milne-Edwards, "by myself in 1827;" and yet Aristotle had said[13] that "whenever Nature is able to provide two separate instruments for two separate uses, without the one hampering the other, she does so, instead of acting like a coppersmith, who for cheapness makes a spit-and-a-candlestick in one.[14] It is only when this is impossible that she uses one organ for several functions."

In conclusion, we may say that the great Stagirite expounded the true principles of science, and that when he failed his failure was caused by lack of materials. His desire for completeness, perhaps, tempted him at times to fill in gaps with such makeshifts as came to his hand; but no one knew better than he did that "theories must be abandoned unless their teachings tally with the indisputable results of observation."[15]

FOOTNOTES:

[3] Pliny, "Natural History," viii. c. 16.

[4] "History of Animals," i. 11.

[5] Bk. iii. 19.

[6] "Meteorology," iv. 7-11.

[7] "History of Animals," i. 16.

[8] "History of Animals," vi. 3.

[9] "On some of the errors attributed to Aristotle."

[10] "History of Animals," i. 17.

[11] See Professor Huxley's article already referred to.

[12] "Aristotle," by G. H. Lewes, p. 325.

[13] "De Part. Anim.," iv. 6.

[14] {obeliskolychnion}.

[15] "De Gener.," iii. 10, quoted by Dr. Ogle.

GALEN.

_GALEN._

Under the Ptolemies a powerful stimulus was given to biological studies at Alexandria. Scientific knowledge was carried a step or two beyond the limit reached by Aristotle. Thus Erasistratus and Herophilus thoroughly investigated the structure and functions of the valves of the heart, and were the first to recognize the nerves as organs of sensation. But, unfortunately, no complete record of the interesting work carried on by these men has come down to our times. The first writer after Aristotle whose works arrest attention is Caius Plinius Secundus, whose so-called "Natural History," in thirty-seven volumes, remains to the present day as a monument of industrious compilation. But, as a biologist properly so called, Pliny is absolutely without rank, for he lacked that practical acquaintance with the subject which alone could enable him to speak with authority. Of information he had an almost inexhaustible store; of actual knowledge, the result of observation and experience, so far as biological studies were concerned, he had but little. This was largely due to the encyclopaedic character of the work he undertook; his mental powers were weighed down by an enormous mass of unarranged and ill-digested materials. But it was due also to the peculiar bent of Pliny's mind. He was not, like Aristotle, an original thinker; he was essentially a student of books, an immensely industrious but not always judicious compiler. Often his selections from other works prove that he failed to appreciate the relative importance of the different subjects to which he made reference. His knowledge of the Greek language appears, too, to have been defective, for he gives at times the wrong Latin names to objects described by his Greek authorities. To these defects must be added his marvellous readiness to believe any statement, provided only that it was uncommon; while, on the other hand, he showed an indefensible scepticism in regard to what was really deserving of attention. The chief value of his work consists in the historical and chronological notes of the progress of some of the subjects of which he treats--fragments of writings which would otherwise be lost to us. Pliny was killed in the destruction of Pompeii, A.D. 79.

Claudius Galenus was born at Pergamus, in Asia Minor, in the hundred and thirty-first year of the Christian era. Few writers ever exercised for so long a time such an undisputed sway over the opinions of mankind as did this wonderful man. His authority was estimated at a much higher rate than that of all the biological writers combined who flourished during a period of more than twelve centuries, and it was often considered a sufficient argument against a hypothesis, or even an alleged matter of fact, that it was contrary to Galen.

Endowed by nature with a penetrating genius and a mind of restless energy, he was eminently qualified to profit by a comprehensive and liberal education. And such he received. His father, Nicon, an architect, was a man of learning and ability--a distinguished mathematician and an astronomer--and seems to have devoted much time and care to the education of his son. The youth appears to have studied philosophy successively in the schools of the Stoics, Academics, Peripatetics, and Epicureans, without attaching himself exclusively to any one of these, and to have taken from each what he thought to be the most essential parts of their system, rejecting, however, altogether the tenets of the Epicureans. At the age of twenty-one, on the death of his father, he went to Smyrna to continue the study of medicine, to which he had now devoted himself. After leaving this place and having travelled extensively, he took up his residence at Alexandria, which was then the most favourable spot for the pursuit of medical studies. Here he is said to have remained until he was twenty-eight years of age, when his reputation secured his appointment, in his native city of Pergamus, to the office of physician in charge of the athletes in the gymnasia situated within the precincts of the temple of AEsculapius. For five or six years he lived in Pergamus, and then a revolt compelled him to leave his native town. The advantages offered by Rome led him to remove thither and take up his residence in the capital of the world. Here his skill, sagacity, and knowledge soon brought him into notice, and excited the jealousy of the Roman doctors, which was still further increased by some wonderful cures the young Greek physician succeeded in effecting. Possibly it was owing to the ill feeling shown to Galen that, on the outbreak of an epidemic a year afterwards, he left the imperial city and proceeded to Brindisi, and embarked for Greece. It was his intention to devote his time to the study of natural history, and for this purpose he visited Cyprus, Palestine, and Lemnos. While at the last-named place, however, he was suddenly summoned to Aquileia to meet the Emperors Marcus Aurelius and Lucius Verus. He travelled through Thrace and Macedonia on foot, met the imperial personages, and prepared for them a medicine, for which he seems to have been famous, and which is spoken of as the _theriac_. It was probably some combination of opium with various aromatics and stimulants, for antidotes of many different kinds were habitually taken by the Romans to preserve them from the ill effects of poison and of the bites of venomous animals.[16]

With the Emperor M. Aurelius he returned to Rome, and became afterwards doctor to the young Emperor Commodus. He did not, however, remain for a long period at Rome, and probably passed the greater part of the rest of his life in his native country.

Although the date of his death is not positively known, yet it appears from a passage[17] in his writings that he was living in the reign of Septimius Severus; and Suidas seems to have reason for asserting that he reached his seventieth year.

Galen's writings represent the common depository of the anatomical knowledge of the day; what he had learnt from many teachers, rather than the results of his own personal research. Roughly speaking, they deal with the following subjects: Anatomy and Physiology, Dietetics and Hygiene, Pathology, Diagnosis and Semeiology, Pharmacy and Materia Medica, Therapeutics.

The only works of this voluminous writer at which we can here glance are those dealing with Anatomy and Physiology. These exhibit numerous illustrations of Galen's familiarity with practical anatomy, although it was most likely comparative rather than human anatomy at which he especially worked. Indeed, he seems to have had but few opportunities of carrying on human dissections, for he thinks himself happy in having been able to examine at Alexandria two human skeletons; and he recommends the dissection of monkeys because of their exact resemblance to man. To this disadvantage may, perhaps, be attributed the readiness, which sometimes appears, to assume identity of organization between man and the brutes. Thus, because in certain animals he found a double biliary duct, he concluded the same to be the case in man, and in one instance he proceeded to deduce the cause of disease from this erroneous assumption.

He supposed that there were three modes of existence in man, namely--

(_a_) The nutritive, which was common to all animals and plants, of which the liver was the source.

(_b_) The vital, of which the heart was the source.

(_c_) The rational, of which the brain was the source.

Again, he considered that the animal economy possessed four natural powers--

(1) The attractive.

(2) The alterative or assimilative.

(3) The retentive or digestive.

(4) The expulsive.

Like his predecessors, he asserted that there were four humours, namely, blood, yellow bile, black bile, and aqueous serum. He held that it was the office of the liver to complete the process of sanguification commenced in the stomach, and that during this process the yellow bile was attracted by the branches of the hepatic duct and gall-bladder; the black bile being attracted by the spleen, and the aqueous humour by the two kidneys; while the liver itself retained the pure blood, which was afterwards attracted by the heart through the vena cava, by whose ramifications it was distributed to the various parts of the body.

Following Aristotle especially, he regarded hair, nails, arteries, veins, cartilage, bone, ligament, membranes, glands, fat, and muscle as the simplest constituents of the body, formed immediately from the blood, and perfectly homogeneous in character. The organic members, _e.g._ lungs, liver, etc., he looked upon as formed of several of the foregoing simple parts.

The osteology contained in Galen's works is nearly as perfect as that of the present day. He correctly names and describes the bones and sutures of the cranium; notices the quadrilateral shape of the parietals, the peculiar situation and shape of the sphenoid, and the form and character of the ethmoid, malar, maxillary, and nasal bones. He divides the vertebral columns into cervical, dorsal, and lumbar portions.

With regard to the nervous system, he taught that the nerves of the senses are distinct from those which impart the power of motion to muscles--that the former are derived from the anterior parts of the brain, while the latter arise from the posterior portion, or from the spinal cord. He maintained that the nerves of the finer senses are formed of matter too soft to be the vehicles of muscular motion; whereas, on the other hand, the nerves of motion are too hard to be susceptible of fine sensibility. His description of the method of demonstrating the different parts of the brain by dissection is very interesting, and, like his references to various instruments and contrivances, proves him to have been a practical and experienced anatomist.

In his description of the organs and process of nutrition, absorption by the veins of the stomach is correctly noticed, and the union of the mesenteric veins into one common _vena portae_ is pointed out. The communications between the ramifications of the vena portae and of the proper veins of the liver are supposed by Galen to be effected by means of anastomosing pores or channels. Although it is evident that Galen was ignorant of the true absorbent system, yet he appears to have been aware of the _lacteals_; for he says that in addition to those mesenteric veins which by their union form the vena portae, there are visible in every part of the mesentery other veins, proceeding also from the intestines, which terminate in glands; and he supposes that these veins are intended for the nourishment of the intestines themselves. Some of Galen's contemporaries asserted that upon exposing the mesentery of a sucking animal several small vessels were seen filled _first_ with air, and _afterwards_ with milk. They had, doubtless, mistaken colourless lymph for air; but Galen ridicules both assertions, and thereby shows that he had not examined the contents of the lacteals. This is somewhat remarkable, because as a rule he omitted no opportunity of determining with certainty, by vivisection and experiments on living animals, the uses of the various parts of the body. As an illustration of this, we have his correct statement, established by experiment, that the pylorus acts as a valve _only_ during the process of digestion, and that it is relaxed when digestion is completed.

He recognizes that the flesh of the heart is somewhat different to that of the muscles of voluntary motion. Its fibres are described as being arranged in longitudinal and transverse bundles; the former by their contractions shortening the organ, the latter compressing and narrowing it. Such statements show that he regarded the heart as essentially muscular. He thought, however, that it was entirely destitute of nerves. Although he admitted that possibly it had one small branch derived from the _nervus vagus_ sent to it, yet he entirely overlooked the great nervous plexus surrounding the roots of the blood-vessels, from which branches proceed in company with the branches of the coronary arteries and veins, and penetrate the muscular substance of the ventricles. He endeavoured to prove, by experiment, observation, and reasoning, that the arteries as well as the veins contained blood, and in this connection he tells an amusing story. A certain teacher of anatomy, who had declared that the aorta contained no blood, was earnestly desired by his pupils, who were ardent disciples of Galen, to exhibit the requisite demonstration, they themselves offering animals for the experiment. He, however, after various subterfuges, declined, until they promised to give him a suitable remuneration, which they raised by subscription among themselves to the amount of a thousand drachmae (perhaps L30). The professor, being thus compelled to commence the experiment, totally failed in his attempt to cut down upon the aorta, to the no small amusement of his pupils, who, thereupon taking up the experiment themselves, made an opening into the thorax in the way in which they had been instructed by Galen, passed one ligature round the aorta at the part where it attaches itself to the spine, and another at its origin, and then, by opening the intervening portion of the artery, showed that blood was contained in it.

The arteries, Galen thought, possessed a pulsative and attractive power of their own, independently of the heart, the moment of their dilatation being the moment of their activity. They, in fact, _drew_ their charge from the heart, as the heart by its diastole _drew_ its charge from the vena cava and the pulmonary vein. The pulse of the arteries, he also thought, was propagated by their coats, not by the wave of blood thrown into them by the heart. He taught that at every systole of the arteries a certain portion of their contents was discharged at their extremities, namely, by the exhalents and secretory vessels. Though he demonstrated the anastomosis of arteries and veins, he nowhere hints his belief that the contents of the former pass into the latter, to be conveyed back to the heart, and from it to be again diffused over the body. He made a near approach to the Harveian theory of the circulation, as Harvey himself admits in his "De Motu Cordis;"[18] but the grand point of difference between Galen and Harvey is the question whether or not, at every systole of the left ventricle, more blood is thrown out than is expended on exhalation, secretion, and nutrition. Upon this point Galen held the negative, and Harvey, as we all know, the affirmative.

The famous Asclepiads held that respiration was for the generation of the soul itself, breath and life being thus considered to be identical. Hippocrates thought it was for the nutrition and refrigeration of the innate heat, Aristotle for its ventilation, Erasistratus for the filling of the arteries with spirits. All these opinions are discussed and commented upon by Galen, who determines the purposes of respiration to be (1) to preserve the animal heat; (2) to evacuate from the blood the products of combustion.

He conjectured that there was in atmospheric air not only a quality friendly to the vital spirit, but also a quality inimical to it, which conjecture he drew from observation of the various phenomena accompanying the support and the extinction of flame; and he says that if we could find out why flame is extinguished by absence of the air, we might then know the nature of that substance which imparts warmth to the blood during the process of respiration.

On another occasion he says that it is evidently the _quality_ and not the _quantity_ of the air which is necessary to life. He further shows that he recognized the analogy between respiration and combustion, by comparing the lungs to a lamp, the heart to its wick, the blood to the oil, and the animal heat to the flame.