102 



PROTEIDS. 



* ^PROTEIDS. 



.' \ 33te^s6- ingr^p ents/a-re the most important constituents of mus- 

 cles, glands, nervous tissue, and blood ; indeed, it has been said 

 of them that none of the phenomena of life occurs without their 

 presence. Of them Gamgee says : " They are highly complex, 

 and, for the most part, uncrystallizable compounds of carbon, 

 hydrogen, oxygen, nitrogen, and sulphur (phosphorus is also some- 

 times present), occurring in a solid, viscous condition, or in solu- 

 tion in nearly all the solids and liquids of the organism. The 

 different members of the group present differences in physical, 

 and to a certain extent even in chemical properties. They all pos- 

 sess, however, certain common chemical reactions, and are united 

 by a close genetic relationship." 



Their percentage-composition is as follows : 



Carbon . 50 to 55 



Nitrogen 15 "18 



Hydrogen 6.9 " 7.3 



Oxygen 20 " 23.5 



Sulphur 0.3 " 2 



qu 

 chl 



When proteids are burned there is found in the ash a certain 

 uantity of salts ; from the ignition of egg-albumin, for instance, 

 chlorids of sodium and potassium result, and salts of calcium, 

 magnesium, and iron. It is still undecided whether these salts 

 are integral parts of proteids or impurities, probably the latter. 



The percentage of proteids in some of the solids and liquids 

 of the body, and their wide distribution, are shown by the follow- 

 ing table : 



Cerebrospinal fluid ....... 0.09 



Aqueous humor 0.14 



Liquor amnii 0.70 



Intestinal juice 0.95 



Pericardia! fluid 2.36 



Lymph 2.46 



Pancreatic juice 3.33 



Synovia 3.91 



Milk 3.94 



Chyle 4.09 



Blood 8.56 



Spinal cord 7.49 



Brain 8.63 



Liver .....; 11.64 



Thymus 12.29 



Muscle 16.18 



Tunica media of arteries .... 27.38 



Crystalline lens 38.30 



Various attempts have been made to ascertain the constitution 

 of the proteids and give a formula for them, but the differences 

 in the results obtained by equally competent chemists have 

 been so great that practically nothing worthy of quoting is on 

 record. There is no doubt, however, that the molecules are very 

 large. 



General Properties of Proteids. All are insoluble in 

 alcohol and ether. They are also said to be soluble with the aid 

 of heat in concentrated mineral acids and caustic alkalies ; but 

 inasmuch as this is accompanied with decompositien of the pro- 



