Emoi men oun kai hê phleps kai tôn allôn hapantôn hekaston dia tên ek tôn tettarôn poian krasin hôdi pôs energein dokei. eisi de ge mên ouk oligoi tines andres || oud' adoxoi, philosophoi te kai iatroi, tô men thermô 8 kai tô psychrô to dran anapherontes, hypoballontes d' autois pathêtika to xêron te kai to hygron. kai prôtos g' Aristotelês tas tôn kata meros hapantôn aitias eis tautas anagein peiratai tas archas, êkolouthêse d' hysteron autô kai ho apo tês stoas choros. kaitoi toutois men, hôs an kai autôn tôn stoicheiôn tên eis allêla metabolên chysesi te tisi kai pilêsesin anapherousin, eulogon ên archas drastikas poiêsasthai to thermon kai to psychron, Aristotelei d' ouch houtôs, alla tais tettarsi poiotêsin eis tên tôn stoicheiôn genesin chrômenô beltion ên kai tas tôn kata meros aitias hapasas eis tautas anagein. ti dêpot' oun en men tois peri geneseôs kai phthoras tais tettarsi chrêtai, en de tois meteôrologikois kai tois problêmasi kai allothi pollachothi tais dyo monais? ei men gar hôs en tois zôois te kai tois phytois mallon men dra to thermon kai to psychron, hêtton de to xêron kai to hygron apophainoito tis, isôs an echoi kai ton Hippokratên sympsêphon; ei d' hôsautôs en || hapasin, ouket' oimai 9 synchôrêsein touto mê hoti ton Hippokratên alla mêd' auton ton Aristotelên memnêsthai ge boulomenon hôn en tois peri geneseôs kai phthoras ouch haplôs alla met' apodeixeôs autos hêmas edidaxen. alla peri men toutôn kan tois peri kraseôn, eis hoson iatrô chrêsimon, epeskepsametha. IV The so-called _blood-making_[29] faculty in the veins, then, as well as all the other faculties, fall within the category of relative concepts; primarily because the faculty is the cause of the activity, but also, accidentally, because it is the cause of the effect. But if the cause is relative to something--for it is the cause of what results from it, and of nothing else--it is obvious that the faculty also falls into the category of the relative; and so long as we are ignorant of the true essence of the cause which is operating, we call it a _faculty_. Thus we say that there exists in the veins a blood-making faculty, as also a digestive[30] faculty in the stomach, a pulsatile[31] faculty in the heart, and in each of the other parts a special faculty corresponding to the function or activity of that part. If, therefore, we are to investigate methodically the number and kinds of faculties, we must begin with the effects; for each of these effects comes from a certain activity, and each of these again is preceded by a cause. IV