30 MODE OF CONDUCTING [iNTROD. 



The first and most important step towards the attainment of 

 physiological knowledge, is, the study of the fabric of the human 

 body. "Et primum," says Haller, "cognoscenda est fabrica cor- 

 poris humani, cujus pene infinitse partes sunt. Qui physiologiam 

 ab anatome avellere studuerunt, ii certe mihi videntur, cum ma- 

 thematicis posse comparari qui machinse alicujus vires et fimc- 

 tiones calculo exprimere suscipiunt, cujus neque rotas cognitas 

 habent, neque tympana, neque mensuras, neque materiam." 



A knowledge of human anatomy alone is, however, not sufficient 

 to enable us to form accurate views of the functions of the various 

 organs. Before an exact judgment can be formed of the functions of 

 most parts of living bodies, Haller says, that the construction of the 

 same part must be examined and compared in man, in various qua- 

 drupeds, in birds, in fishes, and even in insects. And, in proof of the 

 value which attaches to this knowledge of comparative anatomy, he 

 shews how, from that science, it may be determined that the liver 

 is the organ which secretes bile ; and that the bile found in the 

 gall-bladder is not secreted by, but conveyed to, that organ : for 

 no animal has a gall-bladder without a liver, although many have 

 a liver without a gall-bladder ; and, in every case where a gall-blad- 

 der is present, it has such a communication with the liver, that the 

 bile secreted by the latter may be easily transferred to the former. 

 ( ' Vides adeo," he adds, " bilem hepate egere, in quo paretur, vesi- 

 cula non egere, non ergo in vesicula nasci, ex hepate verb in 

 vesiculam transire." 



And Cuvier has happily compared the examination of the com- 

 parative anatomy of an organ, in its gradation from its most complex 

 to its simplest state, to an experiment which consists in removing 

 successive portions of the organ, with a view to determine its most 

 essential and important part. In the animal series we see this 

 experiment performed by the hand of nature, without those dis- 

 turbances which mechanical violence must inevitably produce. We 

 thus learn, from comparative anatomy, that the vestibule is the 

 fundamental part of the organ of hearing; and that the other 

 portions, the semicircular canals, the cochlea, the tympanum and its 

 contents, are so many additions made successively to it, according 

 as the increasing perceptive powers of the animals rendered a more 

 delicate acoustic organ necessary. In a similar manner we learn, 

 that one portion of the nervous system, in those animals in which 

 it has a definite arrangement, is pre-eminently associated with the 

 mental principle, and is connected with, and presides over, the other 

 parts. This organ, the brain, is always situate at the anterior or 



