In convalescence from illness, and also in protracted illnesses, many disturbances occur, some spontaneously and some from things casually administered. I am aware that most physicians, like laymen, if the patient has done anything unusual near the day of the disturbance—taken a bath or a walk, or eaten strange food, these things being all beneficial—nevertheless assign the cause to one of them, and, while ignorant of the real cause, stop what may have been of the greatest value. Instead of so doing they ought to know what will be the result of a bath unseasonably taken or of fatigue. For the trouble caused by each of these things is also peculiar to each, and so with surfeit or such and such food. Whoever therefore fails to know how each of these particulars affects a man will be able neither to discover their consequences nor to use them properly. I hold that it is also necessary to know which diseased states arise from powers and which from structures. What I mean is roughly that a power is an intensity and strength of the humours, while structures are the conformations to be found in the human body, some of which are hollow, tapering Or contracting. from wide to narrow; some are expanded, some hard and round, some broad and suspended, some stretched, some long, some close in texture, some loose in texture and fleshy, some spongy and porous. Now which structure is best adapted to draw and attract to itself fluid from the rest of the body, the hollow and expanded, the hard and round, or the hollow and tapering? I take it that the best adapted is the broad hollow that tapers. One should learn this thoroughly from unenclosed objects i. e. objects that are not concealed, as are the internal organs. that can be seen. For example, if you open the mouth wide you will draw in no fluid; but if you protrude and contract it, compressing the lips, and then insert a tube, you can easily draw up any liquid you wish. Again, cupping instruments, which are broad and tapering, are so constructed on purpose to draw and attract blood from the flesh. There are many other instruments of a similar nature. Of the parts within the human frame, the bladder, the head, and the womb are of this structure. These obviously attract powerfully, and are always full of a fluid from without. Hollow and expanded parts are especially adapted for receiving fluid that has flowed into them, but are not so suited for attraction. Round solids will neither attract fluid nor receive it when it has flowed into them, for it would slip round and find no place on which to rest. Spongy, porous parts, like the spleen, lungs and breasts, will drink up readily what is in contact with them, and these parts especially harden and enlarge on the addition of fluid. They will not be evacuated every day, as are bowels, where the fluid is inside, while the bowels themselves contain it externally; but when one of these parts drinks up the fluid and takes it to itself, the porous hollows, even the small ones, are every-where filled, and the soft, porous part becomes hard and close, and neither digests nor discharges. This happens because of the nature of its structure. When wind and flatulence are produced in the body, the rumbling noise naturally occurs in the hollow, broad parts, such as the bowels and the chest. For when the flatulence does not fill a part so as to be at rest, but moves and changes its position, it cannot be but that thereby noise and perceptible movements take place. In soft, fleshy parts occur numbness and obstructions, such as happen in apoplexy. And when flatulence meets a broad, resisting body, and rushes on it, and this happens by nature to be neither strong so as to endure its violence without harm, nor soft and porous so as to give way and admit it, but tender, fleshy, full of blood, and close, like the liver, because it is close and broad it resists without yielding, while the flatulence being checked increases and becomes stronger, dashing violently against the obstacle. But owing to its tenderness and the blood it contains, the part cannot be free from pain, and this is why the sharpest and most frequent pains occur in this region, and abscesses and tumours are very common. Violent pain, but much less severe, is also felt under the diaphragm. For the diaphragm is an extended, broad and resisting substance, of a stronger and more sinewy texture, and so there is less pain. But here too occur pains and tumours. There are many other structural forms, both internal and external, which differ widely from one another with regard to the experiences of a patient and of a healthy subject, such as whether the head be large or small, the neck thin or thick, long or short, the bowels long or round, the chest and ribs broad or narrow, and there are very many other things, the differences between which must all be known, so that knowledge of the causes of each thing may ensure that the proper precautions are taken. As I have said before, we must examine the powers of humours, and what the effect of each is upon man, and how they are related to one another. Let me give an example. If a humour that is sweet assumes another form, not by admixture, but by a self-caused change, what will it first become, bitter, or salt, or astringent, or acid? I think acid. Therefore where sweet humour is the least suitable of all, acid humour is the next least suitable to be administered. Because:— 
 (1) Health is a crasis of all the humours, none being in excess; 
 (2) Sweet humour passes readily into acid; 
 (3) Therefore, when sweet is the least suitable as a remedy (there being an excess of it already), acid (which is likely to be reinforced from the sweet) is the next least suitable. 
 Kéhlewein’s text makes sense only if we transpose ὀξύς and γλυκύς . If you want ὀξὺς χυμός for crasis you can get it best by adding ὀξύς , next best by adding γλυκύς , which naturally turns into ὀξύς . If a man can in this way conduct with success inquiries outside the human body, he will always be able to select the very best treatment. And the best is always that which is farthest removed from the unsuitable. APPENDIX ON CHAPTER XX, p. 54. οἰνος ἄκρητος πολλὸς ποθεὶς διατίθησί πως τὸν ἄνθρωπον· καὶ πάντες ἄν αἱ εἰδότες τοῦτο γνοίησαν, ὅτι αὕτη δύναμις οἲνου καὶ αὺτὸς αἴτιος . So A; other MSS. have ἀσθενέα after ἄνθρωπον, ἰδόντες for οἱ εἰδότες, ἡ after αὕτη and ἐστιν after αὐτός . This passage contradicts the general argument, which is that in medicine statements about foods must not be made ἁπλῶς . Cheese is not bad food; it is only bad in certain conditions, and in certain ways, and at certain times. In these circumstances cheese has a δύναμις which does not belong to cheese in itself, but is latent until certain conditions call it forth. The error, says the writer, is not made in the case of wine. Everybody knows that in itself wine is not bad; it is drinking to excess, or at wrong times, which is mischievous. Now the reading of A (in fact any MS. reading) makes the writer say that wine itself is to blame ( αὐτὸς αἴτιος )—an obvious contradiction of the general argument. My colleague the Rev. H. J. Chaytor most ingeniously suggests that αὐτός refers not to wine but to the man. He would therefore translate this δύναμις of wine and the man himself are to blame. But not only is it more natural for αὐτός to refer to wine, but the writer’s whole point is that in and by itself no food is αἴτιος . A food is a cause only in certain conditions, or, rather, certain conditions call forth certain δυνάμεις . I think, therefore, that the right reading is ὅτι τοιαύτη δύναμις οἵνου καὶ οὐκ αὐτὸς αἵτιος . Such and such a δύναμις of wine ( i. e. a δύναμις caused by excess of wine acting upon the human φύσιις ) is to blame and not mere wine by itself. ὅτι τοιαύτη might easily turn into ὅτι αὕτη , and the omission of οὐ by scribes is not uncommon. There is an attractive vigour about the reading ἰδόντες for οἱ εἰδότες , and it may be correct. Anybody can see at a glance that in the case of wine it is excess, etc., and not merely wine itself which is to blame.