ALBUMINS OR PROTEINS. 137 



or clupein, and 20-25 milligrams of sturine, per kilo weight of the animal, 

 are sufficient to kill a dog. It is still undecided whether this poisoning is 

 due to the protamines or to some admixture. 



Besides the protamines mentioned, cyclopterine * from the lump-fish, 

 (Cyclopterus lumpus), and acipenserine, from the testes of the sturgeon 

 (Acipenser stellatus), 2 are also described as protamines. Two other pro- 

 tamines may be mentioned: a- and ^-cyprinine, 3 which are obtained from 

 the sperm of the carp (Ciprinus carpio). The sperm of the brook-trout 

 (Salmo fario), the white snapper (Coregonus oxyrhynchus) , the sheath- 

 fish (Silurus glanus), and the pike (Esox lucius), 4 also contain protamines. 

 Protamines have not been isolated positively from any other representa- 

 tives of the animal kingdom. The significance of the protamines has not 

 yet been established. 



Related to the proteins just described is a group of albuminous bodies, 

 whose biological significance differs materially from that of any so far 

 mentioned. Their common properties have united the heterogeneous 

 substances into one group, called the " albuminoids." They constitute 

 the frame- work of the animal tissues. They are not found in the cell pro- 

 toplasm, nor in the tissue fluids. We shall see later, that their significance 

 also corresponds to their entire composition. They are not to be considered 

 as nutrient materials in the narrower sense, and participate but little in the 

 intermediate metabolism. Incidentally they are difficultly digestible; 

 in fact, being somewhat resistant to the digestive ferments. The albu- 

 minoids are to the animal body what the higher carbohydrates (for 

 instance, cellulose) are to the vegetable. They are all insoluble in 

 water and salt solutions. They are only slightly attacked by acids and 

 alkalies. It is practically useless to attempt to purify the albuminoids. 

 They can only be studied in the manner in which they occur in nature. 

 It is an entirely arbitrary assumption that they exist as a chemical 

 entity. 



Collagen occupies a special position among the albuminoids. It con- 

 stitutes the foundation of the bones and cartilages, and constructs the 

 fibrils of the connective tissues. It may be extracted from these tissues 

 by boiling with water. The product which goes into solution is called 

 glue, glutin, or gelatin. In contra-distinction to the other proteins, 

 collagen is soluble in warm water, and solidifies on cooling. Numerous 

 investigations indicate that it is not an individual substance, undoubtedly 

 differing according to the animal, or organ, from which it is obtained. 

 The nature of the change underlying the formation of gelatin has 



1 N. Markowin: Z. physiol. Chem. 28, 313 (1899). 



2 D. Kurajeff: Z. physiol. Chem. 32, 197 (1901). 



8 A. Kossel and H. D. Dakin: ibid. 40, 565 (1903), loc. cit. 

 4 A. Kossel: find. 22, 176 (1896), loc cit. 



