6 INTRODUCTION: THE FIELD AND PROBLEMS OF BIOLOGY 



accuracy of observations and the validity of the conclusions drawn from 

 them. 



It is also important to keep in mind that science and the scientific 

 method have limitations. From its very nature science is man-made; 

 it has rejected any thought or expectation of a Mount Sinai, whence 

 absolute truth can be received with final authority. Such authority as 

 it has is due to the consensus of its accepted practitioners and to the 

 fact that it provides the most accurate account of its phenomena that 

 man has yet discovered. Moreover, from a practical standpoint, it is 

 often difficult to know where fact and proved principle leave off and 

 hypothesis begins. Indeed, scientific facts are often partial and incom- 

 plete, having been selected and understood because they appeared to 

 answer the question in mind at the time they were chosen and verified. 

 Further, as we have already said, science assumes that the phenomena 

 with which it deals are related and that there is a definite orderliness in 

 nature. This assumption lies back of all science, and in a strict sense is 

 probably incapable of proof. Even if this assumption can be accepted 

 as true, science can hope only to answer questions of "how" — not ques- 

 tions of "why" unless we are to define "why" in terms of "how." And 

 finally, as Sir Francis Bacon pointed out centuries ago, we must "ask 

 nature fair questions." Many questions that we propose unwittingly take 

 for granted conditions that do not exist. For example, the old question, 

 " How (or why) does the seeing of a rabbit by a pregnant woman cause a 

 harelip in her child?" is "unfair," because it has assumed an unproved 

 affirmative answer to an unrecognized antecedent question, "Does seeing 

 a rabbit cause harelip in the child?" 



The development of the "cell doctrine" — an example of the growth 

 of a hypothesis into a principle. We shall soon be concerned with cells, 

 and their roles in the structure, functioning, development, and inheritance 

 of the organism. It is therefore pertinent to use the growth of the modern 

 cell doctrine, or cell principle, to illustrate the steps by which accumula- 

 tion of facts may lead to formulation of a hypothesis, and the hypothesis 

 become established as an accepted principle. 



1. The Accumulation of Observations. This step began soon after the 

 invention of the microscope, and was doubtless long retarded by the slow 

 development of satisfactory microscopes. Robert Hooke (1635-1703) 

 first observed cellular structure in cork and other plant tissues; he named 

 the small spaces he saw cells, because they looked like little rooms. 

 Malpighi (1628-1694), in Italy, made many microscopic studies of in- 

 sects, plants, and human tissues. He remarked on the "repeated vesicles" 

 that seemed to make up many of the tissues he examined. Other students 

 of plant and animal structures from time to time saw and mentioned that 

 various parts of their specimens were composed of microscopic units, 



