THE PROTEIDS. 55 



that analogous bodies also occur in plants. It appears quite prob- 

 able that the paranucleinic acid of the egg-yolk represents the ante- 

 cedent of the true nucleinic acids of the growing embryo. Osborne 

 suggests that both may be ethers of a pentahydroxyl phosphoric 

 acid H 5 PO 5 or its first anhydride, H 8 P 2 O 7 . 



Wildenow further speaks of a phosphorus-containing substance 

 which she obtained from casein, and which, like the true nucleinic 

 acids, precipitated albumin. This has been confirmed by Salkowski, 

 who isolated the substance and gives the following values as express- 

 ing its elementary composition: C = 31.9, H = 4.43, N = 9.72, 

 and P = 2.55. 



THE PROTEIDS. 



The proteids are conjugate albumins in which an albuminous 

 group is united with a nuclein, a nucleinic acid, or a pigment radicle. 

 The group comprises the nucleoproteids, the nucleins, and the haemo- 

 globins. 



The Nucleoproteids. The nucleoproteids are the most impor- 

 tant constituents of nuclear structures and represent highly differ- 

 entiated albumins, which are intimately concerned in the various 

 manifestations of cell-life. They are characterized by their phos- 

 phorus content and the fact that on hydrolysis they all give rise to 

 the formation of xanthin bases, pyrimidin derivatives, and pentoses. 

 These in turn are derived from the nucleinic acid component of the 

 nucleoproteids, which in turn may be directly combined with the pri- 

 mary albuminous radicle, or indirectly as a uuclein, viz., as an unsat- 

 urated nucleoproteid, within the larger group. These relations are 

 shown in the following schema : 



Nucleoproteid (second order) 



Albumin Nucleinic acid Albumin Nuclein 



Albumin Nucleinic acid 



From this it will be seen that both nucleins and nucleinic acids 

 are derivatives of the nucleoproteids. They can be isolated from 

 their mother-substance, but do not occur in nature as such. The 

 nucleins are split oif and precipitated on digestion with pepsin- 

 hydrochloric acid, or by treating with acids and alkalies, by boiling 

 with water, etc. 



Detailed investigations into the structure of the complex nucleo- 

 proteids, in which an albuminous radicle is in combination with a 

 nuclein, are still wanting, so that it is impossible to make any defi- 

 nite statements regarding the albuminous group in either the nuclein 

 complex or in the nucleoproteid as a whole. In the simpler bodies, 

 on the other hand, which have been obtained from the testicles of 

 various fishes the albuminous component is apparently always a 



