104 PHYSIOLOGY 



lable 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 metaprotein and albumoses and glucosamine. 

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

 of galactosamine. 



With the raucins may be classified certain bodies which have been derived from 

 ovarian cysts, namely, pseudomucin and paramucin. Pseudomucin occurs as a con- 

 stituent 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. Paramucin 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 w r hich may be 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. Chondro- 

 mucoid 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 substance chondrosin, which is certainly an ammo- 

 derivative of a polysaccharide 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 ' lar- 

 daceous 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 precipitated by boiling diluted egg-white. From 

 the filtrate 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. 



(10) THE ALBUMINOIDS OR SCLERO-PROTEINS. Under this heading 

 are grouped a number of diverse substances which play an important part 

 in building up the framework of the body. Their value as skeletal tissue 

 seems to be determined by their insoluble character. On this account it is 

 practically impossible to speak of purifying them. In every case we can 

 simply take the residue of a skeletal tissue which is left after extraction of 

 the soluble constituents. When broken down by the action of strong acids, 

 they yield a series of disintegration products which are included among those 

 we have already studied as the disintegration products of proteins. Their 

 difference from the proteins which are employed in metabolism for their 



