x8 THE HISTORY OF BIOLOGY 



of the body was due to the existence and commingling of these four primary- 

 elements; if they existed in the proper proportions, health was the result; 

 if the harmony between them was disturbed, sickness followed.^ For the 

 rest, Hippocrates and his successors seem to have shared the conception 

 which originated in Heracleitus that the soul, the life -principle, consists 

 of fire or — in later writings — of substance akin to fire, called pneuma 

 (breath). 



In regard to human anatomy, osteology was, as has been mentioned, 

 comparatively carefully studied. The skull in particular was radically in- 

 vestigated and a large number of the names of its bones and sutures are 

 derived from these works. The bones of the face were also minutely studied. 

 The knowledge of the backbone was more defective, while, on the other 

 hand, the bones of the extremities were well described. Of the muscles sev- 

 eral, particularly the muscles of the extremities, are correctly described, 

 though the actual muscle substance is not accurately distinguished from a 

 number of other internal organs. The separate parts of the digestive canal 

 are named, but their connexion and function were extremely vaguely known. 

 The various sections of the intestinal tube are given different names and char- 

 acteristics in the different writings on the subject. The liver is an organ 

 which particularly interested the people of antiquity, as also the spleen, but 

 there were very confused ideas of their respective functions. A good deal 

 was known about the glands, especially the lymphatic glands; the pancreas, 

 on the other hand, was unknown. The function of the glands was believed 

 to be to segregate water from the body. Of the respiratory organs the larynx 

 and the trachea in particular were completely described, while the lungs 

 were treated only summarily. Respiration is believed to serve the purpose 

 of cooling the heart. Again, in another treatise it is asserted that the inhaled 

 air spreads to the various parts of the body, to the brain, the body cavity, 

 and the arteries. The enunciation of the circulatory system is, as mentioned 

 above, vague. The different cavities of the heart are fairly accurately de- 

 scribed, but here exists already the delusion which it has since been so dif- 

 ficult to eradicate that the left cavity of the heart does not contain 

 blood, but some kind of airy substance, which is proved by reference to 

 slaughtered animals, in which the arterial blood is drained off by severing 

 the jugular veins! The apprehension of the venous system is far vaguer than 

 that of the heart, and, moreover, the description of the former in the differ- 

 ent Hippocratic treatises is highly contradictory. The right side of the heart 



2 The doctrine of the four temperaments, which counts for something even in our own day, 

 is based originally on the theory of these four juices and their distribution in the body; in san- 

 guine people the predominating factor is the blood, in phlegmatic people the phlegm, in choleric 

 people the yellow and in melancholy people the black bile. Melancholy, owing to its origin in 

 the black bile, is called spleen or atrabiliousness. 



