Z36 THE HISTORY OF BIOLOGY 



work he defines physiology as " animata anato??ie," a vitalized anatomy, and 

 it is in fact the phenomena of life that he seeks to discover in his special 

 investigations. The most remarkable of these is without doubt his treatise 

 on the irritable and sensible parts of the body, which he published simul- 

 taneously in several languages. In this investigation he first establishes the 

 fact that the organs of the body are partly irritable, partly non-irritable; 

 why this is so, science cannot discover; it can only show that it is so. As 

 irritable (jnitahilis) he mentions such a part of the body as contracts upon 

 being touched; as sensible (sensibiUs), again, he defines a part of the body, 

 contact with which induces an impression in the mind. Which organs belong 

 to the one or the other category is a question which can be answered 

 only by experiment. The performing of such experiments on live animals 

 Haller finds highly revolting, but in the interests of truth it cannot in this 

 case be avoided. Thus he has proved that, of the two layers of skin, the 

 epidermis is non-sensitive, the cutis on the other hand has feeling, and adi- 

 pose tissue is non-sensitive. Muscles are sensible, but this is due not to the 

 actual muscular substance, but to the nerves which are in connexion there- 

 with; the tendons, again, are non-sensible, because they are not connected 

 with nerves. Bones and periosteum are insensible, the cerebral membrane, 

 the peritoneum, and the veins likewise. The intestines are sensible, but not 

 the liver, the spleen, or the kidneys. Irritability exists in muscles, but is 

 induced through the nervous system; thus the diaphragm has been made 

 to contract by irritating a severed nerve. Therefore the irritability cannot 

 have anything to do with the mind, for that is indivisible. Haller then enu- 

 merates a number of irritable organs — veins, intestines, sexual organs. Fi- 

 nally he discusses the question of what it is that induces irritability. Muscle 

 is composed of lime and earth; if it is asked which component part is irritable, 

 the answer must be the lime. Lastly he deals with the question of vital 

 organs, which serve the unconscious manifestations of life, and voluntary 

 organs, which serve the will. 



The investigation here referred to must without doubt be regarded as 

 one of those that have led biology into new directions. Not only the scheme 

 of the work, but also the method of presentation he employs and the con- 

 clusions he draws are each of fundamental importance; irritability and sen- 

 sibility are facts, which hold true to this very day,^ and the experimental 

 method by means of which the phenomena have been established is still 

 used today. There occur, indeed, in the examples just given one or two actual 

 mistakes — thus the peritoneum is, as a matter of fact, sensible and the in- 

 testines insensible — while the actual theoretical treatment suffers from the 



^ Instead of irritability the characteristic property of muscle is nowadays termed "con- 

 tractility." Haller's irritability theory was later applied without distinction to various organs 

 in the body, thereby causing considerable confusion. 



