THE CONSTRUCTION OF PROTEINS 163 
3. Mera-PRoTEINS.— These are insoluble in distilled 
water or in solutions of neutral salts. They are readily 
soluble in very dilute acids and alkalies, and their solutions 
do not coagulate on boiling. They are precipitated by care- 
fully neutralising their solutions, and when they are boiled 
in the resulting state of suspension they are converted into 
coagulated protein, and will not re-dissolve on the addition 
of either dilute acid or alkali. 
They are readily prepared from either albumins or 
globulins by warming them in the presence of a little acid 
or alkali, preferably at about 60°C. Alkali-albumin may 
be prepared by acting on albumin with fairly strong caustic 
potash in the cold. 
The meta-proteins are not of frequent occurrence in 
plants, but may be met with in certain seeds. 
4, Prorzoses or Aupumoses.—These are generally 
soluble in distilled water, though some are less so than 
others. They can be precipitated from their solutions by 
saturating the latter with neutral ammonium sulphate, 
They differ from the members of the first two classes by 
not being converted into coagulated protein on boiling. 
Their characteristic reaction is that they give with nitric 
acid, or with potassium ferrocyanide in the presence of acetic 
acid, a precipitate which dissolves on warming the liquid 
and reappears as it cools. Unlike any of those of the 
preceding groups, they -have the property of dialysing 
through a parchment membrane, but only very slowly. 
5. Peprones.—These are much like albumoses, but do 
not give a precipitate with nitric acid or with potassium 
ferrocyanide in the presence of acetic acid. They are not 
precipitated by saturation of their solutions with ammo- 
nium sulphate, nor are they coagulated on boiling. Their 
power of dialysis is much greater than is that of the 
proteoses. 
Neither peptones nor proteoses occur very plentifully 
in plants, and they are probably formed in them only from 
the decomposition of the more stable forms of globulin and 
