GENERAL CONSIDERATIONS. IT 



and other experimentalists of the present generation, fur- 

 nishes abundant proof that the faculty of observation and the 

 power of generalization are not necessarily inconsistent with 

 each other. 



It would be futile to attempt to point out all the difficul- 

 ties and sources of error in experimentation on living animals. 

 These must be overcome by the physiologist after he has 

 become practically acquainted with them. It must be borne 

 in mind, however, that we are interrogating Nature ; and 

 our sole aim must be to put our questions intelligently and 

 interpret the answers correctly. She does not unfold her 

 mysteries to the careless and inconsiderate observer. An 

 accident may lead the reflecting student to frame a particular 

 set of experiments, for the explanation of an unexpected 

 phenomenon ; but we should go to work with an idea of what 

 we wish to know, always ready to correct or abandon our 

 most cherished preconceived notions if we find they are not 

 in accordance with facts. Experiments should not be isolat- 

 ed. A golden opportunity is thrown away if we stop short 

 of the end in a legitimate series of investigations ; for none 

 are better fitted to go through the later steps of a natural 

 series of experiments than they who have conceived and 

 executed the first. 



With the many varying conditions of the system which 

 inevitably occur in living animals, it is almost unnecessary to 

 add that an important observation should be repeatedly con- 

 firmed, and the answer to our experimental inquiries obtained, 

 if possible, in different ways; It must be remembered that 

 Nature never contradicts herself, and has no exceptions. 

 Her laws are invariable ; and if experiments are apparently 

 contradictory, we must look for differences in the conditions 



shortly after he had commenced the publication of the fourth volume in 1855. The 

 prolegomenes, and the sections on digestion, absorption, the blood, respiration, 

 and circulation, are perhaps the most candid, exhaustive, and best considered 

 essays on these subjects in any language. Science suffered a great loss when 

 the author was thus cut off in the midst of his labors. 

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