548 POPULAR SCIENCE MONTHLY. 



residue of tlie alcoliolic extract was too liigli for tlie body to be 

 protagon, as bad previously been supposed. He put bis pupils 

 Manassien and Diakonow on tbis problem. Tbe former quickly 

 found tbe substance to be not protagon, but lecitbin, a peculiar 

 nitrogenous pbospborized fat, and tbe latter laid bare tbe cbemical 

 nature of tbis substance. Hoppe-Seyler bimself proceeded to ex- 

 amine otber cells for tbe presence of lecitbin and cbolesterin, and 

 soon recognized tbat tbese substances, as well as tbe albumins, potas- 

 sium pbospbate, and glycogen, must be considered ever-present con- 

 stituents of protoplasm. Hoppe-Seyler furtber sbowed tbat tbe 

 lecitbin generally existed in tbe cell, not free, but in combination 

 witb albumin. Tbis fact drew Hoppe-Seyler's attention to similar 

 compounds wbicb are formed by albumin combined witb otber sub- 

 stances, and he proposed for sucb bodies tbe name " proteids," a 

 name wbicb tbey bave subsequently borne. 



Tbe discovery of lecitbin drew attention to tbe organic compounds 

 of pbospborus in protoplasm. Tbere were many indications tbat 

 tbe nuclei contained sucb a substance, altbougb tbe difficulties in 

 its isolation bad bitberto been insurmountable. His pupil Miescber 

 was placed on tbis problem, and discovered tbe " nucleins," probably 

 tbe most important constituents of protoplasm tbus far recognized. 

 Hoppe-Seyler bimself discovered " vitellin," tbe first of tbe pseudo- 

 nucleins, and casein was soon sbown to bave a similar pbospborized 



radicle. 



In tbe cbemistry of respiration Hoppe-Seyler was personally 

 active, and formulated a bypotbesis of tbe cbemical nature of 

 respiration and living matter wbicb is practically tbe only well- 

 grounded tbeory of its kind extant, and one wbicb bas seldom been 

 surpassed for brilliancy. By a stroke of genius be correlated tbe 

 newly discovered reducing powers of protoplasm witb its oxidizing 

 powers, and recognized tbe essential identity of tbe processes of life 

 and putrefaction. Tbis idea tbrew ligbt on many pbases of cellular 

 metabolism. It was first briefly mentioned in tbe IlediciniscJie- 

 chemische Untersuchungen in 18Y1. It was clearly stated in 

 volume xii of Pflliger's ArcUv fur die gesammte Physiologie some 

 years later, and forms tbe kernel of most of bis subsequent work. 



Tbe oxygen of tbe air, as is well kno^vn, is in a molecular or inert 

 state, and not in an atomic form. It is unable, in tbis form, to 

 carry out tbe oxidations of protoplasm. To do tbis it must be first 

 made "active," eitber by conversion into ozone or by having its 

 molecule split. Hoppe-Seyler's tbeory of respiration turns on the 

 fact tbat in protoplasm and in putrefying masses, reducing 

 substances are formed wbicb are able to split tbe oxygen mole- 

 cule, setting free atomic oxygen. In this manner, if only air 



