THE PROTEINS 117 



animals, and is secreted either by the goblet cells of the epithelium or 

 by special groups of cells collected together to form a mucous gland. 

 They may be precipitated from their solutions or semi-solutions by 

 the addition of acids, and after precipitation need the addition of 

 alkalies for their re-solution. They are not coagulable by heat. The 

 presence of their protein moiety causes them to give the various 

 typical protein tests, such as the xanthoproteic, Millon's, the biuret 

 reaction, and so on. Prolonged boiling with acids splits the molecule, 

 with the production of acid albumin and albumoses and glucosamine. 

 From the mucin of frogs' eggs a similar treatment results in the produc- 

 tion of galactosamine. 



With the mucins may be classified certain bodies which have been derived 

 from ovarial cysts, namely, pseudomucin and paramucin. Pseudomucin occurs 

 as a constituent of the colloid material from ovarian tumours. It forms slimy 

 solutions which do not coagulate by heat and are not precipitated by acetic 

 acid. It is precipitated by alcohol, the precipitate being soluble in water even 

 after standing a long time under the alcohol. On boiling with acid it gives 

 a reducing substance. Paramuciu differs from the above in reducing Fehling's 

 solution before boiling with acids. Otherwise it resembles pseudomucin. 

 Leathes, in investigating this body, isolated from it a reducing substance which 

 apparently was an amino -derivative of a disaccharide, perhaps in combination 

 with glycuronic acid. 



The mucoids include a number of substances which mav be 



tt 



extracted from various tissues by the action of weak alkalies, e.g. from 

 tendons, bone, and cartilage. The best studied example of this group 

 is the chondromucoid which, with collagen, forms the ground substance 

 of cartilage. Chondromucoid is especially rich in sulphur and gives 

 protein by long treatment with weak alkali. On boiling for a short 

 time with acid it is decomposed into sulphuric acid and chondroitin, 

 and this latter, on further action of the acid, is converted into a sub- 

 stance chondrosin, which is certainly an amino-derivative of a poly- 

 saccharide containing the elements of glycuronic acid and an amino- 

 disaccharide. Chondroitin-sulphuric acid occurs not only in cartilage 

 but also in bone, yellow elastic tissue, white fibrous tissue, and as a 

 constant constituent of the lardacein or amyloid substance which 

 occurs as a deposit in the middle coat of the blood-vessels as the 

 result of syphilis or long-continued suppuration, and gives rise to the 

 condition known as ' lardaceous disease.' Another example of this 

 class of mucoids is ovomucoid, which is a constituent of egg-white. 

 In order to prepare ovomucoid the globulin and albumin are pre- 

 cipitated by boiling diluted egg-white. From the nitrate ovomucoid 

 can then be thrown down by alcohol. A similar body has been 

 prepared from blood serum. Both these mucoids yield a large amount 

 of reducing substance on hydrolysis. Thus from 100 grm. of ovo- 

 mucoid it is possible to prepare 30 grm. of glucosamine. 



