6 



GENERAL PHYSIOLOGICAL METHOD 



tions. Extirpation and transsection represent important methods of research 

 in studying the functions of the central nervous system. It cannot be denied 

 however that the results of excision methods are unfortunately too often 

 very difficult of explanation, and that their interpretation is not infrequently 

 made still more difficult by unintentional lesions. 



3. EXPERIMENTS ON SURVIVING ORGANS 



In the cold-blooded animals many organs remain alive for a long time 

 after the death of the organism, even when they have been cut out of the body. 

 By virtue of this property it has been possible to collect a great mass of most 

 important facts. Our knowledge of the general properties of nerve and muscle 

 rests for the most part on experiments with exsected organs. Organs removed 



FIG. 1. Illustrating the use of the graphic method in recording the simple contraction of a 

 frog's muscle. For description, see text. 



from the body remain still longer alive if, as was first done by Ludwig and his 

 school, they be artificially nourished with blood. Under such conditions it is 

 possible also to maintain organs of warm-blooded animals alive for a consid- 

 erable time after death of the body as a whole. Organs removed from the 

 body which remain capable of activity are called surviving organs. 



4. THE GRAPHIC METHOD 



Functions of organs are not infrequently expressed by outward move- 

 ments of some kind, which as a rule are so rapid that their details cannot be 

 followed by the naked eye. They can be studied very exactly, however, if 

 one can hit upon a method by which the movements record themselves upon a 

 moving surface (graphic method, Ludwig, 1847). 



Since this method finds very wide application in most branches of physiol- 



