122 HOW CEOPS GROW. 



or less complex derivatives of the bases Pyridin, C 5 H 5 N, 

 and Quinolin, C 9 H 7 ST, which are colorless, volatile 

 liquids with sharp, unpleasant odor, produced from albu- 

 minoids at high temperatures, and existing in smoke, 

 bone-oil and tar. The alkaloids bear to these bases simi- 

 lar relations to those subsisting between the amines and 

 ammonia. 



8. PHOSPHORIZED SUBSTANCES. This class of bodies 

 are important because of their obvious relations to the 

 nutrition of the brain and nerve tissues of the animal, 

 which have long been known to contain phosphorus as 

 an essential ingredient. All our knowledge goes to show 

 that phosphorus invariably exists in both plants and ani- 

 mals as phosphoric acid or some derivative of this acid, 

 or, in other words, that their phosphorus is always 

 united to oxygen as in the phosphates, and is not directly 

 combined to carbon, hydrogen, or nitrogen. 



Nuclein. This term is currently employed to desig- 

 nate various imperfectly-studied bodies that resemble the 

 albuminoids in many respects, but contain several per 

 cent of phosphorus. They are easily decomposable, 

 boiling water being able to remove from them phosphoric 

 acid, and under the action of dilute acids they mostly 

 yield phosphoric acid, albuminoids and hypoxanthin, 

 C 5 H 4 N 4 0, or similar imide bases. They are very difficult 

 of digestion by the gastric juice. The nucleins are found 

 in the protoplasm and especially in the cell-nuclei (see 

 p. 245), of both plants and animals, and have been ob- 

 tained from yeast, eggs, milk, etc. , by a process based on 

 their indigestibility by pepsin. Chemists are far from 

 agreed as to the nature or composition of the nucleins. 



Lecithin, C 44 H 90 NP0 9 . This name applies to a num- 

 ber of substances that have been obtained from the brain 

 and nerve tissue of animals, eggs and milk, as well as 

 from yeast, and the seeds of maize, peas, and wheat. 

 The lecithins are described as white, wax-like substances, 



