THE NITROGENOUS SUBSTANCES 77 



4. Cytosin, 6.amino-2.oxy-pyrimidin, 



NH C.NH a 

 OO CH 

 NH CH 



(Kossel) has an equally wide distribution. 



5. In nearly all of the nucleic acids there is a carbohydrate, sometimes a 

 pentose(l-xylose), sometimes a hexose. 



Nothing definite is known concerning the manner in which phosphorus is 

 combined in the nucleic acids. 



One can obtain a fair idea of the complexity of nucleic acids from the follow- 

 ing structural formula for a-guanylic acid given by Bang. 



OH OH 

 C 5 H 4 N 6 0-P-0-C 8 H 6 (OH). C 6 H 9 6 



Guanin X Glycerin Pentose 



C 6 H 4 N 6 -0-P-0-C 3 H 6 (OH). C 6 H 8 6 

 ,H 5 (OH). C 6 H 8 6 

 3 H 6 (OH).C 6 H 9 6 



OH^OH. 



The simplest nucleins are the saltlike compounds of nucleic acids with the 

 protamins and histons. These simple proteids are closely related chemically, and 

 there seems to be a close relationship physiologically as well; for whereas one* 

 finds histons in unripe fish sperm, in the ripe sperm protamins are found. 



The nucleins finally unite with proteid to form nucleo-proteids, which, it 

 appears, occur in (dead) cell protoplasm and especially in the (dead) cell 

 nucleus, where Miescher first demonstrated them. Their composition is very 

 complicated, and they represent the first decomposition products of the living 

 substance thus far known. Some of them appear to contain iron. 



D. Chondro-proteids. Compounds of proteid with chondroitin-sulphuric 

 acid (C 18 H 27 ]SrS0 17 Schmiedeberg) and found in the mucoid of cartilage, 

 amyloid, in tendon mucin, and presumably in other mucous substances. 



C. SUBSTANCES RESEMBLING PROTEIDS 



The following substances are known to be closely related to proteids, from 

 the fact that on decomposition they yield in general the same substances as do 

 proteids. It is possible that some of them should be enumerated among the 

 true proteids. 



A. Protamins (see page 70). 



B. Keratin, a substance rich in sulphur (2.5-5 per cent) ; amorphous, in- 

 soluble in water, alcohol, ether and the digestive fluids; contained in horn, 

 epidermis, hair, nails, etc. On heating with water in closed tubes it yields 

 albumoses and peptones. It develops the characteristic smell of burnt horn 

 when ignited. 



