SPECIAL REACTIONS OF THE ALBUMINS. 45 



amino-acids are present in the different substances in somewhat 

 different quantitative proportions. To these variations the varying 

 properties of the different substances are no doubt due. Noteworthy 

 is the absence of glycocoll in serum-albumin and egg-albumin, and 

 of tyrosin and tryptophan in glutin. Most remarkable is the extra- 

 ordinary predominance of the diamino-acids in the protamins and 

 the low values found in the albuminoids. Note further the high 

 value of glycocoll and alanin in silk fibroin, and of cystin in 

 keratin. The percentage values of the resolved portion of the 

 different albumins, when compared with our knowledge of a few 

 years ago, show a most encouraging advance all along the line, but 

 also disclose deep gaps which must yet be bridged. 



Molecular Size. Our knowledge of the molecular size of the 

 protein molecule is as yet very imperfect, and the figures given 

 should only be regarded as approximative, minimal values : 



Casein 6,660 



Serum-albumin 5,100 



Serum-globulin 4,600 



Egg-albumin 4,900 



Edestin 7,300 



Oxyhsemoglobin 14,800 



Proto-albumose 2,500 



Siegfried's peptones 260-280 



For cystallized egg-albumin Hofmeister calculated the formula 

 C 2 , 9 H 386 N 58 S 2 O 78 , which would correspond to a weight of 5378. 



Classification of the Albumins. A satisfactory classifica- 

 tion of the proteins upon a chemical basis is not yet possible, and 

 we are hence forced to adhere to their old division into groups, 

 which is essentially based upon their gross physical properties. We 

 accordingly divide them into five classes, viz., the native albumins, 

 the nucleo-albumins, the proteids, the albuminoids, and the derived 

 albumins. These can be subdivided further as follows : 



I. The native albumins : 



1. The albumins proper (serum-albumin, egg-albumin, 



lactalbumin). 



2. The globulins (serum-globulin, fibrinogen, ovoglobulin, 



myosin, myogen, lactoglobulin, various cell-globulins, 

 and vegetable globulins). 



3. The gluco-albumins (mucins, mucoids, helicoproteid). 



4. The keratins. 



5. The histons. 



6. The protamins. 



II. The nucleo-albumins (casein, the vitellins, phytovitellins, the 

 nucleo-albumins of the cell-protoplasm, mucinous 

 nucleo-albumins). 

 III. The proteids : 



1. The nucleoproteids (compounds of nucleinic acid with 



(a) histon, (b) protamin, (c) other albumins. 



2. The hemoglobins (compounds of a histon with haamatin). 



