CHAPTER III 



CONCERNING METHODS OF PHYSIOLOGICAL ANALYSIS 



IN THE attempt to throw light on the problems of development many 

 methods have been developed and employed and have given a large 

 body of evidence. Since the mature organism is the result of develop- 

 ment, it, as well as earlier stages, has been used as material in attacks on 

 problems of development, but the data obtained are of interest chiefly in 

 the light of what is learned from earlier stages. Some consideration of 

 these methods, their objects, their limitations, and particularly some of the 

 difficulties involved and the precautions necessary appears desirable as a 

 preliminary to discussion of results obtained with them. 



METHODS FOR DETERMINING RESPIRATION 



Since the axial developmental gradients appear to involve protoplasmic 

 activity of some kind and since respiration, as determined by oxygen con- 

 sumption and carbon dioxide production, is a measure of certain proto- 

 plasmic activities and, to greater or less degree, an indicator of others, the 

 question at once arises whether differences in rate of respiration bear any 

 relation to the gradients or to other features of developmental pattern. 

 Unfortunately, most of the methods available at present for direct deter- 

 mination of respiratory rate are rather unsatisfactory for the purpose of 

 determining whether such differences exist, because they make it necessary 

 to separate different regions of the body and to determine respiration in 

 the isolated pieces. This procedure introduces various difficulties and com- 

 plicating factors, some of which cannot be entirely overcome or avoided ; 

 but if they are not considered and ehminated or controlled as far as possi- 

 ble, the results obtained are without definite significance. When an or- 

 ganism, particularly an animal, is separated into pieces for determinations 

 of respiratory rate of different regions along an axis, several questions 

 arise: First, is respiratory rate altered in consequence of section? Second, 

 if alteration occurs, is the rate increased or decreased? Third, are pieces 

 from different levels of the axis affected to the same degree by section? 

 Fourth, if alteration of rate occurs after section, is it persistent or tem- 

 porary? Fifth, if the alteration is temporary, does the rate sooner or later 



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