SECT. I] PHYSICO-CHEMICAL SYSTEM 271 



observed that raw egg-white was quite non-reactive towards the 

 nitroprusside test for sulphydryl groups, but that immediately upon 

 coagulation by heat it became vividly reactive, and gave an intense 

 purple colour. This change only took place in conditions where 

 denaturation of the protein was involved, and Harris suggested that 

 this treatment might unmask a thiopeptide linkage or some similar 

 arrangement which by hydrolysis or keto-enol transformation would 

 give rise to an active sulphydryl group in the resulting metaprotein 

 molecule. Later, Harris found that only 14 per cent, of the sulphur 

 in ovoalbumen could be accounted for as cystine, so that some un- 

 known sulphur compound must be present in considerable quantity, 

 and an exactly similar finding was later reported by Osato for the 

 egg-membrane protein of the herring. The cystine recoverable from 

 serum albumen, on the other hand, accounted for 86 per cent, of 

 the sulphur there. The possibilities of these facts with relation to the 

 metabolism of the embryo have not yet been explored. Philothion, 

 according to de Rey-Pailhade, exists in the egg-white of the hen 

 but not in that of the duck. 



The principal investigation of ovomucoid is that of Morner. He 

 had previously discovered that percaglobulin, a protein extracted 

 from the unripe ovarial fluid of the perch {Perca fluviatilis) would 

 precipitate ovomucoid from its solution. With this reagent he made 

 an examination of a wide variety of birds' eggs, in order to study 

 the distribution of ovomucoid. By direct estimation he found it to 

 be present in all the eggs he studied, but it seemed to exist in two 

 sharply distinguished forms, one which would give a precipitate with 

 percaglobulin, and another which would not. Thus the hen [Gallus 

 domesticus) with i -46 per cent, of ovomucoid gave a highly positive 

 reaction, but the hawk {Astur palumbarius) with i -45 per cent, gave 

 none at all. Preparations of ovomucoid from the two varieties of 

 egg-white (see Table 10 a) did not show up the existence of two ob- 

 viously different chemical individuals, and it was concluded that the 

 preparations were in each case mixed with a small amount of the 

 other substance. Moreover, of the egg-whites which gave a positive 

 reaction with percaglobulin, some contained ovomucoid precipitable 

 with Esbach's reagent (e.g. Clangula glaucion and Somateria mollissima) 

 and others contained an ovomucoid which could not be so pre- 

 cipitated (e.g. Gallus domesticus and Podiceps cristatus). It is quite 

 uncertain how many of the effects observed by Morner are due to 



