the Echinoderm Egg during Fertilisation. 227 



It is, of course, possible that the dipeptide is present in considerable 

 quantity in the eggs and sperm in the oxidised (disulphide) form, and that 

 during fertilisation it undergoes reduction. It has, of course, long been 

 known that the hydrogen ion concentration of the sea-water exercises a 

 marked influence on the uptake of oxygen by the egg of the sea-urchin. 

 Thus Warburg (13) found that an increase in the HO concentration in the sea- 

 water in which the eggs of Strongylocentrotus were placed from 10 -8 to 10 -3 

 increased the oxygen consumption of the eggs from 1*4 to 8'1. Hopkins 

 finds that glutathione in the oxidised form is rapidly reduced by fresh 

 tissues, but that this reduction is greatly accelerated if the reaction or P H of 

 the medium is well on the alkaline side of neutrality, while an acid reaction 

 greatly retards this reduction. In a similar manner the oxygen uptake of the 

 egg-cell is accelerated by alkali and retarded by acids. 



That the glutathione is readily washed out of the eggs is shown by a 

 slight pink colour the wash-water gives by the nitro-prusside test. In 

 certain experiments in which the unfertilised eggs were treated so that their 

 glutathione was washed out, I could find no trace of respiratory power on 

 the part of these washed eggs. The same eggs unwashed showed well- 

 marked respiration. The oxygen consumption of the unfertilised egg is so low, 

 however, that it is perhaps unfair to assume on this ground that glutathione 

 is the sole body concerned in the respiration of the ovum. Prof. Hopkins 

 has been so kind as to undertake certain experiments with washed 

 egg material for me, and he tells me that on the addition of glutathione to 

 these egg preparations, the reduction of this in the presence of fresh tissue 

 was markedly greater in the case of the fertilised washed eggs than in the 

 case of the unfertilised. There seems to be fairly substantial ground then 

 for believing that there is an immediate increase in the quantity of this 

 remarkable body in the ovum on fertilisation. 



It has been mentioned that cystin is one of the amino-acids entering into 

 the composition of glutathione ; it is interesting to note that Warburg (16) 

 has recently drawn attention to the fact that cystin, absorbed on the surface 

 of carbon particles, is capable of considerable respiration, taking up oxygen 

 and giving off carbon dioxide. He found that one gram of blood carbon dis- 

 solved in a similar weight of a 1/500 N cystin solution, took up the same 

 quantity of oxygen as a similar weight of liver tissue. The carbon-cystin 

 system, moreover, under the action of oxygen, gives the same end-products 

 as the combustion of egg-white, that is carbon dioxide, ammonia and 

 sulphuric acid. 



There are a number of other interesting points brought up by the presence 

 of glutathione in the germ-cells of the sea-urchin and the possible rdle it 



