Dr. Buchanan on the White or Opaque Serum of the Blood. 231 



more complicated than in plants, and maj require the co-operation of 

 various organs. 



It is at present a matter of doubt among physiologists whether the 

 primary nutritious liquid prepared by the digestive organs, is intro- 

 duced into the blood through the lacteals, or through the branches 

 of the portal vein. It cannot, however, be doubted, that when the nu- 

 tritious matter is first absorbed, it is in the liquid state. It is re- 

 markable, therefore, that it should be found afterwards in the blood 

 as a precipitate, or in the solid state. It may, however, be readily con- 

 ceived how this effect will be produced, when we reflect, that the food 

 is dissolved in the stomach by an acid liquid ; which, if absorbed by the 

 veins of the stomach, will, on mingling with the blood, be at once ren- 

 dered alkaline, and will therefore let fall whatever substances its 

 acidity enabled it to dissolve. This reasoning, however, is no longer 

 applicable, if we suppose the white matter of the blood to be derived 

 from the admixture with it, of the alkaline chyle. A different ex- 

 planation was suggested to me by Dr. R. D. Thomson. He supposed 

 that the white matter of the serum might be soluble in it at blood- 

 heat, just as the urate of ammonia and other sediments which often 

 appear in the urine upon cooling, are held in solution at the natural 

 heat of the body. On trying the effect of artificial heat, we found that 

 the serum became considerably clearer, but it was still opaque. 



It may also be supposed, that the serum is capable of dissolving 

 a certain quantity of white matter, but after being saturated, deposits 

 any superfluous portion. In confirmation of this view, I may remark, 

 that the relative quantity of serum and crassamentum lias an effect on 

 the tint of the serum. Two individuals who had dined upon gelatin, 

 had each the serum opaline, at the end of the third hour after the meal : 

 after six hours the opaline tint was merely somewhat deeper in the 

 one case, while in the other the serum was as opaque as I ever saw it ; 

 but on comparing the quantity of serum obtained from the same 

 measure of blood in these two cases, it was found to be more abundant 

 by one half in the former case than in the latter. 



If any additional evidence be required of the origin of the white 

 colour of the serum of the blood, it may be derived from an experiment 

 of Hewson, from which so acute a reasoner could certainly never have 

 drawn any other than the right conclusion, had it been one of his first 

 experiments ; but it was not made till his mind was thoroughly blinded 

 by his theory of re-ahsorbed fat, and he in consequence misinterpreted 

 it Hewson had found that geese had very commonly white serum, 

 though their chyle was always transparent ; and he therefore chose to 

 make his experiment on them. " I therefore" says he, " took two of 

 them that were very hungry, and feeding both of them with oats, one I 

 killed four hours after, when I knew a part of the oats were undigested, 

 and upon examining the blood, I found the serum whitish, and full of 

 small globules ; on its being suffered to stand a little time, the white 



