CHEMIC COMPOSITION OF THE HUMAN BODY. 35 



tive tissue and in bone. When the tendons of muscles, the 

 ligaments, or decalcified bone are boiled for several hours, 

 the collagen and ossein are converted into soluble gelatin, 

 which, when the solution cools, becomes solid. 



(c) Chondrigen. This is supposed to be the organic basis of 



the more permanent cartilages. When they are boiled, they 

 yield a substance which gelatinizes on cooling, and to which 

 the name chondrin has been given. 



(d) Elastin is the name given to the substance composing the 

 fibers of the yellow, elastic connective tissue. 



(e) Keratin is the substance found in all horny and epidermic 



tissues, such as hairs, nails, scales, etc. It differs from most 

 proteids in containing a high percentage of sulphur. 

 (/) Nuclein. This is an amorphous substance obtained from the 

 nuclei of both animal and vegetable cells. The chief con- 

 stituent appears to be nucleic acid. Chemic analysis shows 

 that nuclein contains not less than three per cent, of phos- 

 phorus. On boiling with strong alkalies, nuclein is partially 

 decomposed, yielding a proteid resembling globulin and phos- 

 phoric acid. A nucleo-proteid is a compound of nuclein and 

 a proteid. 



The average percentage composition of several proteids is shown 

 in the following analyses: 



c. H. N. o. s. 



Egg-albumin, 52.9 7.2 15.6 23.9 0.4 (Wiirtz). 



Serum-albumin, 53.0 6.8 16.0 22.29 1.77 (Hammersten). 



Casein, 53.3 7.07 15.91 22.03 0.82 (Chittenden and Painter). 



Myosin, 52.82 7.11 16.77 21.90 1.27 (Chittenden and Cummins). 



The molecular composition of the proteids is not definitely known, 

 and the formulae which have been suggested are therefore only 

 approximative. Leow assigns to albumin the formula C 72 H 112 N 18 - 

 O 22 S, while Schiitzenberger raises the numbers to C 240 H 392 N 65 O 75 S 3 , 

 either of which shows that the proteid molecule is extremely complex. 

 As a class, the proteids are characterized by the following properties : 



1. Indiffusibility. None of the proteids normally assumes the 



crystalline form, and hence they are not capable of diffusing 

 through parchment or an animal membrane. Peptone, a product 

 of the digestion of proteids, is an exception as regards its diffu- 

 sibility. As met with in the body, all proteids are amorphous, 

 but vary in consistence from the liquid to the solid state. The 

 colloid character of the proteids permits of their separation and 

 purification from crystalloid diffusible compounds by the process 

 of dialysis. 



2. Solubility. Some of the proteids are soluble in water, others in 



solutions of the neutral salts of varying degrees of concentration, 



