EXPERIMENTS ON LIVING ANIMALS 5 



As for the rest, physiology must create its own methods according to the 

 nature of the problems to be solved ; and in the following presentation of the 

 functions of the body we shall discuss as far as may be necessary for our 

 present purposes the methods in use. There are however some general methods 

 of physiological technique which it will be appropriate to discuss in this place. 



2. EXPERIMENTS ON LIVING ANIMALS 



It is true that one can obtain important information concerning the 

 functions of the organs and of the entire body without any operative inter- 

 ference indeed, all of our direct observations on man have been made under 

 such circumstances. But it is often necessary to make the organs accessible 

 to immediate observation. We are therefore often compelled to perform on 

 living animals many kinds of operations, some of which put the skill and 

 inventive genius of the operator to a severe test. In these operations the 

 animals are as a rule anaesthetized with ether, chloroform, chloral, morphine 

 or some other narcotic. Only if the purpose of the experiment makes it neces- 

 sary is the operation performed on un-ansesthetized animals. For many physi- 

 ological purposes the animal must be observed for a long time after the end of 

 the operation, and in such cases it is necessary to use the antiseptic and aseptic 

 methods of surgery with every possible care. Furthermore, it is many times 

 of advantage in the experiment to suppress the voluntary movements of the 

 animal, and this is done by administering the American arrow poison, curare. 

 Since this drug paralyzes the respiratory muscles along with others it is 

 necessary to resort to artificial respiration, which is usually accomplished by 

 rhythmically forcing into the lungs with a bellows a quantity of air suitable 

 to the size of the animal. The air is introduced through the trachea by 

 means of a cannula connected with the bellows. In all operations where 

 the pleural cavities must be opened artificial respiration is indispensable 

 (Vesalius, about 1540). 



After the animal has been prepared in this way, the particular experiment 

 follows. It would be impossible to describe here even in condensed form the 

 different principles of experimentation which must be observed if perfectly 

 unequivocal results are to be obtained. The following may be given as an 

 illustration : 



There are in general only two ways of discovering the influence of the 

 central nervous system on a given organ or function : either the nerve supply- 

 ing that organ may be cut and the effects on the behavior of the organ noted, 

 or the nerve may be stimulated artificially and the resulting action of the 

 organ be determined. In most cases the latter method gives the clearer results, 

 for mere section of the nerve cannot give us any definite conclusions, unless 

 the nerve at the moment it was cut was actually transmitting impulses from 

 the central system, which of course is by no means always the case. 



It is often of great profit, in determining the physiological importance 

 of an organ, to extirpate it, and to maintain the animal alive. The resulting 

 absence of certain phenomena frequently permits of very valuable conclusions. 

 Especially is this true in the case of organs like the thyroid gland and the 

 adrenal bodies, which to direct observation disclose no sign of their func- 



