CHEMICAL BASIS OF THE ANIMAL BODY. 1169 



various sizes and finally minute needles, either aggregated or 

 separate, make their appearance. It has not as yet been found 

 possible to obtain these so-called crystals from solutions which 

 have been freed by dialysis from the ammonium salt. 



2. Serum-albumin. 



This is the sole proteid, apart from the globulins, which 

 occurs in serum. Pure solutions of this proteid closely re- 

 semble those of egg-albumin in their general reactions, but 

 the difference of the two is clearly shewn by the following 

 statements. 



1. When free from salts and in 1 — 1-5 p.c. solution it 

 coagulates on heating to 50°. The addition of sodium chloride 

 raises the coagulating point to 75 — 80°. Under the condi- 

 tions in which it occurs in serum it is not found to shew any 

 opalescence on heating at any temperature below 60°, and it 

 may be regarded as coagulating completely at 75°. 



By fractional heat-coagulation of serum freed from globulin, evi- 

 dence has been obtained of the existence in the serum of many ani- 

 mals of three albumins coagulating at 70 — 73°, 77 — 78°, and 82 — 85°. 

 In some serums only two of these albumins occur. 



2. It is not readily coagulated by alcohol or precipitated by 

 ether: egg-albumin is, and most readily by alcohol. 



3. It is more strongly lsevo-rotatory than egg-albumin. 



4. It is not very readily precipitated by strong hydro- 

 chloric acid and the precipitate is readily soluble on the further 

 addition of acid: the reverse is the case for egg-albumin. 



5. Precipitated or coagulated serum-albumin is more readily 

 soluble in nitric acid than is egg-albumin. 



6. Egg-albumin if injected subcutaneously or into a vein, 

 reappears unaltered in the urine; serum-albumin similarly 

 injected does not thus normally pass out by the kidney. 



Serum-albumin is found not only in blood-serum, but also 

 in lymph, both that contained in the proper lymphatic channels 

 and that diffused in the tissues; in chyle, milk, transudations, 

 and many pathological fluids. 



It is this form in which albumin generally appears in the 

 urine. 



Class II. Derived Albumins (Albuminates). 

 1. Acid-albumin. 



When a native albumin in solution, such as egg- or serum- 

 albumin, is treated for some little time with a dilute acid, such 

 as hydrochloric, its properties become entirely changed. The 

 most marked changes are (1) that the solution is no longer 



74 



