SECT. 3] AND ORGANISATION 589 



undergone by the head and tail fragments. The younger the embryo 

 the more readily the tissues disintegrated and cytolysed during an 

 experiment. The heads containing the large watery brain vesicles 

 cytolysed very quickly and gave a wholly abnormal respiratory rate, 

 but the tail fragments, being composed of less deHcate material, did 

 not undergo cytolysis so quickly. Whenever you get any cytolysis 

 the oxygen consumption is of course greatly increased." Shearer 

 afterwards extended the work with Barcroft microrespirometers to 

 planarian head and tail fragments, and absolutely failed to get the 

 results which should have been found on the Child theory. Here the 

 position was compHcated by muscular movement which did not go 

 on to the same extent in the head and tail fragments. The situation 

 is therefore at present a deadlock, and we are at a standstill until 

 further accurate work on the lines already laid down by Shearer is 

 carried through. 



Practically no importance can be attached to the experiments 

 which have been made with potassium permanganate and indo- 

 phenol blue. Child & Hyman in 19 19 placed embryos in very 

 dilute solutions (Af/ 10,000) of potassium permanganate, and de- 

 scribed in all cases a gradient along the cephalocaudal axis with 

 maximum activity, i.e. maximum reduction of the permanganate, 

 at the anterior end. Similar work was afterwards done by Child 

 (on Corella), by Galigher, and by Hyman. As a demonstration of 

 contributory interest the permanganate method has its value, but it 

 is far too uncertain biochemically to serve as the basis for the 

 identification of axial with metaboUc gradients in embryos. As for 

 the indophenol blue reaction, Child applied it to the development 

 of the starfish egg, and observed that the apical third or half of the 

 body of blastula and gastrula stages was always stained a deep blue 

 before the blastopore region had become stained at all. In his 

 1924 book he stated that exactly similar gradients had been observed 

 with methylene blue, reduction of this dye being faster at the cephalic 

 than at the caudal end of the embryo. These observations cannot 

 by any means permit of conclusions about gradients of metabolic 

 rate. 



These criticisms of one of the main aspects of Child's theory are 

 essentially the same as those made by Parker and by Loeb in his book 

 on Regeneration. "The unit for the measurement of metabolism", 

 said Loeb, acidly, "is the calorie, and the calories produced by an 



