EXPERIMENTAL EQUIPMENT AND PROCEDURES 



growth rate of Rana pipiens tadpoles ". Thus, if the investigation proves that no re- 

 lation exists, even the negative data will be significant. 



Further, one cannot anticipate that the results will be encompassed by the orig- 

 inal statement of purpose. But the more specific and succinct is the original state- 

 ment of purpose, the more clear-cut will be the entire research program. 



MATERIALS: There are two major classes of inaterial that may be used in experimental 

 embryology, or any experimental procedure in biology, namely (a) Biological and 

 (b) Physical and/or Chemical. 



One should list species or strain of animal used, as well as age, sex, and num- 

 bers. If it is an embryonic stage, that should be properly defined. 



One should list all of the chemicals and apparatus that are to be used so that any- 

 one attempting to repeat this experiment can do so under identical conditions. 



EXPERIMENTAL PROCEDURE: In this section one must outline exactly what he intends 

 to do. 



a. The controls. 



b. The number, age, sex stage of development, or other conditions of the animals 

 or embryos. 



c. The single experimental variable imposed. 



d. The method of collecting data. 



THE CONTROLS : Every experiment, every research project, must include a "con- 

 trol" or "controls. It is difficult to conceive of a situation in which a control is 'not 

 possible, and most experiments are not valid without adequate controls. 



The control is the standard, the normal, the untreated organism or situation with 

 which experimentally induced results are to be compared. One simply cannot evalu- 

 ate experimental data without controls, without organisms or embryos exactly iden- 

 tical but without the imposed experimental variable. Only by direct comparison of 

 an experimental situation with a control situation can we evaluate any deviations 

 caused by the experimental variable. 



The ideal control, in any animal experiment, is a genetically identical individual, 

 if such is obtainable. Identical twins, derived from the same zygote by cell separa- 

 tion at the two-cell stage, would therefore be ideal in the sense that one could be re- 

 garded as the exact (genetic) biological duplicate of the other. One could be kept 

 protected from the single variable of interest while the other could be subjected to it, 

 to determine the effect. Isolation cultures among the protozoa or bacteria, resulting 

 in clones which may be separated and followed, all derived from a single parent, 

 would constitute ideal experiinental material. This is because these unicellular 

 forms have asexual reproduction, the progeny resulting from binary fission and there- 

 fore being identical with each other as well as with the single parent. 



Among multicellular forms, and all embryos, this ideal situation is generally 

 impractical so that we usually satisfy the condition of a control with litter mates, de- 

 rived from the same parents and at the same time. Certainly these are not genetic- 

 ally identical, but nonetheless, they are more closely identical than any other possible 

 combination of paired individuals. 



Thus, while one's interest may be directed toward the effect ol some experimen- 

 tal variable, he cannot even recognize his results if he does not have proper and 

 adequate controls with which to compare. The CONTROL is absolutely essential to 

 every experin^ient. 



The novice might ask about controls for extirpation or transplantation experi- 

 ments. Obviously, if an extirpation results in a specific organ loss, the control 

 would be an extirpation from another region to determine whether there results a 

 similar organ loss. Likewise, in transplantations there is the donor tissue and the 

 location in the host field, either condition wliich must have a control to specifically 



