CYTOCHEMICAL TESTS ON EMBRYOS 343 



This procedure seems at first a bit crude and yet very accurate results can be obtained. 

 The reactions in the procedure are as follows: 



MnCl2 + aNaOH = Mn(OH)2 + ZNaCl 



4MN(OH)2 + O2 = 2Mn203 + 4H2O 



Mn203 + 6HC1 = 2MnCl2 + 3H2O + CI2 



CI2 + 2KI = 2KC1 + I2 



Therefore, for each molecule of O2 present, two molecules of It are liberated. In titrat- 

 ing, the free iodine reacts with the sodium thiosulphate to form tetrathionate and sodium 

 iodide as follows: 2Na2S20T + I2 " Na2S40^ + 2Nal, which are both coloreless, allow- 

 ing the end point to be determined by the disappearance of the blue color that forms when 

 iodine reacts with the starch indicator. 



Once this procedure is stabilized, and the student has achieved reproducible results, it 

 is suggested that the following additional tests be made: 



1. Oxygen consumption at various stages of development, particularly during a 

 series of early cleavages and at gastrulation. 



2. Effect of cyanide, dinitrophenol, iodoacetate, colchicine. 



3. Effect of low and of high pH. 



4. Effect of temperature over definite time interval. 



5. Oxygen consumption of artificially activated eggs (parthenogenetic) and of andro- 

 genetic eggs. 



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