56 SECTIONAL ADDRESSES. 



been considered by some to be identical. Elementary analysis shows 



no difierence : 



C H N S P 



Cow . . . 52-96 705 15-65 0.758 0-847 



Sheep . . . 52-92 7-05 15-60 0771 0809 



and individual amino-acids are obtained in the same amounts after 

 hydrolysis. After racemisation, however, Dudley and Woodman found 

 the tyrosine from cow's caseinogen to be wholly inactive, that from the 

 sheep fully active. In the former animal the tyrosine is probably inside 

 the molecule, in the latter it is on the periphery. We are thus able to 

 discover differences in the intimate pattern of the molecule. Dakin and 

 Dale connected these differences with antigenic specificity. Crystallised 

 albumins from the whites of hens' and ducks' eggs are very similar and 

 seem to be composed of the same units in equal amounts, but Dakin 

 found that three amino-acids, leucine, aspartic acid, and histidine, behave 

 differently to alkali in the two molecules, and appear to occupy different 

 places. Hen's albumin has some aspartic acid but no leucine or histidine 

 on the periphery ; duck's albumin, on the other hand, has no aspartic 

 acid, but some leucine and histidine on the outside of the molecule. By 

 the very sensitive anaphylactic reaction of the isolated guinea pig's uterus, 

 Dale showed that the two proteins are specifically different as antigens. 

 Differences in arrangement, even of the same amino-acids, help to differ- 

 entiate the proteins of various species. It is on the diversity of the 

 proteins that the difference of species is based. 



Another recent example of the application of organic chemical theory 

 to biology is due to Stedmau. Having traced the miotic action of 

 physostigmine to a urethane grouping, he synthesised a number of ure- 

 thanes of simple dimethylamino phenols, e.g. R.NH.CO.O.C6H.4N(CH3)2. 

 The physiological activities of the tertiary bases is generally in the 

 order ortho and para > meta, but on conversion into quarternary salts the 

 ortho and para become less active, the meta more so and the order is 

 meta > ortho or para. This recalls the reactivities of disubstituted 

 benzene derivatives, which have of late been studied in connection with 

 the polarity theory. 



Whilst organic chemists are often eager to investigate the constitution 

 of animal and vegetable substances, they are less ready to undertake the 

 preUminaries of purification and isolation, and are therefore less apt to 

 discover new ones. By esterification and by the use of a high vacuum 

 Emil Fischer made the monamino acids amenable to fractional distilla- 

 tion, a standard operation of organic chemistry. He discovered several 

 new members of the group. But most substances of physiological interest 

 require a special technique, on the development of which the biochemist 

 may spend much labour. Thus Kossel showed how to separate the 

 purine and pyrimidine bases of the cell nucleus, and the important 

 diamino-acids, histidine, arginine, and lysine. Hopkins, by his special 

 reagent, was able to isolate tryptophane, the parent substance of indigo, 

 long after indigo itself was being manufactured synthetically. Dakin 

 found that monoamino acids can be extracted from aqueous solution 

 by butyl alcohol, and using this new technique and Foreman's method 



