38 PR0TE1DS OF THE SERUM. 



to 64*5' (Starke). It is changed into syntonin or acid-albumin by the action of 

 dilute HC1, and by dilute alkalies into alkali-albuminate. 



Serum -albumin is absent from the blood of starving snakes ; and reappears after they are 

 fed (TV-// . 



[Serum-Albumin r. Egg- Albumin. Although serum-albumin is closely related to egg- 

 albumin ihey differ (a) as regards their action upon polarised light ; (6) the precipitate pro- 

 duced by adding HC1 or HN0 3 is readily soluble in 4 c.c. of the reagent in the case of serum- 

 albumin, while the precipitate in egg-albumin is dissolved with very great difficulty ; (c) egg- 

 albumin, injected into the veins, is excreted in the urine as a foreign body, while serum-albumin 

 is not ; (rf) serum-albumin is not coagulated by ether, while egg-albumin is, if the solution is 

 not alkaline ( 249). Serum albumin has never been obtained free from salts, even when it is 

 dialvsed for a very long time.] 



After all the serum -globulin in serum is precipitated by magnesium sulphate, serum-albumin 

 still remains in solution. If this solution be heated to 40 or 50 C. a copious precipitate of 

 non-coagulated serum-albumin is obtained, which is soluble in water. If the serum-albumin be 

 filtered from the fluid, and if the clear fluid be heated to over 60 C, Fredericq found that it 

 becomes turbid from the precipitation of other proteids ; the amount of these other bodies, 

 however, is small. 



[Proteids of the Serum. Halliburton has shown by the method of "fractional 

 heat-coagulation" (i.e., ascertaining the temperature at which a proteid is 

 coagulated, filtering the fluid and again heating the filtrate to a higher temperature), 

 that from the same fluid perhaps two or more proteids, all with different tempera- 

 tures of coagulation, may be obtained. Care must be taken to keep the reaction 

 constant. He finds that serum-globulin coagulates at 75 C, while serum-albumin 

 in reality consists of three proteids, which coagulate at different temperatures ; (a) 

 at 73, (/?) at 77, and (y) at 84 C] 



[Precipitation by Salts. Sulphate of magnesia not only precipitates serum-globulin but also 

 fibrinogen. The fluid must be shaken for several hours to get complete saturation. Sodic 

 sulphate, when added to serum deprived of its globulin by MgS0 4 , precipitates serum-albumin, 

 but it produces no precipitate with pure serum. In this way serum-albumin may be obtained 

 in a pure, uncoagulated, and still soluble condition. Serum-globulin is thrown down by sodic 

 nitrate, acetate, or carbonate ; while all the proteids of the serum are precipitated by potassic 

 acetate or phosphate, and the same result is brought about by adding two salts, e.g., MgS0 4 

 and Na,S0 4 (in this case sodio-inagnesic sulphate is formed); MgS0 4 and NaN0 3 ; AIgS0 4 and 

 KI ; NaCl and Na.,S0 4 . After serum-globulin is thrown down by MgS0 4 , the addition of 

 MgS0 4 and Na. 2 S0 4 or the double-salt, precipitates the serum-albumin, which is still soluble in 

 water. As sulphate of ammonia precipitates all the proteids except peptones, it may be used 

 (Halliburton).] 



[The plasma of Invertebrata (decapod crustaceans, some gasteropods, cephalopods, &c.) clots 

 like vertebrate blood, and contains fibrinogen, but, in addition, there is found in it a substance 

 corresponding to luemoglobin, and called by Fredericq, hamiocyanin. It exists like Hb in two 

 conditions, one reduced and the other oxy-hsemocyanin, the former being colourless, the latter 

 blue. In its general characters it resembles Hb, although it contains copper instead of iron, 

 and gives no absorption-bands (Halliburton). In the blood of some decapod crustaceans there 

 is a reddish pigment, tetronerythrin, which is identical with that in the exoskeleton and 

 hypoderm. It belongs to the group of lipochromes, like some of the pigments of the retina. 

 The ha-mocyanin is respiratory in function, and it is remarkable that it is contained in the 

 plasma, and not in the formed elements like the Hb of vertebrates. So that, stated broadly, 

 in these invertebrates the plasma is both nutritive and respiratory in its functions, while in 

 Vertebrates the red corpuscles chiefly are respiratory and the plasma nutritive.] 



II. Fats (0*1 to 0-2 per cent.). Neutral fats (tristearin, tripalmitin, triolein) 

 occur in the blood in the form of small microscopic granules, which, after a meal 

 rich in fat (or milk) render the serum quite milky. 



[The amount of fat in the scrum of fasting animals is about 0*2 per cent. ; during digestion 

 0-4 to 6 per cent; and in dogs fed on a diet rich in fat it may be 1'25 per cent. There are 

 also minute traces of fatty acids (succinic). Riihrig showed that soluble soaps, i.e., alkaline 

 salts of the fatty acids, cannot exist in the blood. Cholesterin may be considered along with 

 the fats. It ocenrs in considerable amount in nerve-tissues, and, like fats, is extracted by ether 

 from the dry residue of blood-serum. Hoppe-Seyler found 0*019 to 314 per cent, in the serum 

 of the blood of fattened geese. There is no fat in the red blood-corpuscles. Lecithin (its de- 

 composition-products, glycerin -phosphoric acid and protagon) occur in serum and also in the 

 blood-corpuscles.] 



