I. AVOID FRUITLESS EXPERIMENTS 27 



the humidity remains constant at each point in the system. A similar 

 difficulty is met with regard to the uniformity of any of the several 

 factors that may be subject to regulation, whether it be the concentra- 

 tion of the chemical constitutents of the medium or the absorption of 

 radiant energy at various depths in a tissue. 



In experimental research, where an attempt is made to achieve 

 control of numerous variable factors, it would appear only logical to 

 make the observations objectively Avherever possible. In fact, this has 

 been done rather widely. For certain classes of observations this 

 striving for objectivity can be pushed to the point of diminishing re- 

 turn. It would be quite uneconomical, for instance, to insist that all 

 data be recorded automatically. 



Photographic observations are quite readily made and conse- 

 quently have played a valuable role as scientific evidence. In the use 

 of the biophysical methods discussed m this volume, however, the 

 photographic evidence itself will usually require an objective quanti- 

 tative analysis. A case in point is the densitometric analysis of 

 photographic negatives for various purposes. Although comparisons 

 are often made subjectively, a distinct advantage is gained by using 

 an objective type of microphotometer. Automatic recording equip- 

 ment is becoming increasingly available so that such variables as 

 temperature, hydrogen ion concentration, and atmosphei'ic gas com- 

 position can be continuously registered during an experiment. The 

 same is true of a number of electrical quantities. Especially valuable 

 in this connection is the use of cathode ray oscillographs for recording 

 transient phenomena. For light measurements, the use of a ther- 

 mopile or photocell together with a recording galvanometer has made 

 it easy to eliminate the subjective factor. Motion picture photog- 

 raphy is becoming increasingly useful. 



The weaknesses of photoelectric and photographic methods of 

 recording information must not be glossed over lightly, however. 

 They can yield biased data. Insufficient attention has been given to 

 their shortcomings on the part of some biologists in the past. The 

 color sensitivity of a photocell may differ markedly in wavelength 

 range and in relative value from that of the human eye, for example ; 

 and books have been written to explain what every scientist needs to 

 know about the behavior of photographic emulsions. 



3. Enij>loy Standard Units of Measurement 



During the exploratoiy stage of research in a new field, it often 

 happens from necessity that many measurements are made which are 



