20 Dr. A. Leared on the presence of Sulp ho cyanides [June 17, 



shows that while the sulphocyanide naturally present in the serum is 

 capable of combining with added iron, the serum possesses the power of 

 preventing the formation of sulphocyanide of iron when both compounds 

 are added and intermixed with it. 



An analogous masking of chemical action is described by Bernard. 

 He found that when a solution of lactate of iron is mixed with serum, and 

 a solution of cyanide of potassium is then added, prussian blue is not 

 formed, as would be the case if the solutions were mixed in water instead 

 of serum. 



I have not been able to decide positively whether the sulphocyanide is 

 or is not confined to the serum. Analysis, after combustion, is unsuitable, 

 because sulphocyanides are formed in the combustion of organic matter. 

 But so far as I have been able to determine from the maceration of the 

 clot in water, the sulphocyanides exist only in the serum. 



The foregoing facts point either to the presence of free sulphocyanic 

 acid, or of sulphocyanide of potassium, or sodium, or of both, in the serum 

 of the blood. This leads to the consideration of that much-vexed question, 

 the cause of the red colour of the blood. So far as concerns exact colour, 

 nothing more closely resembles blood than a solution of sulphocyanide of 

 iron. This is prima facie evidence that red blood owes its colour to the 

 iron compound. The iron is known to be localized in the globules. These 

 are surrounded by a fluid containing sulphocyanic acid in a combination 

 which easily yields the acid when required. Such is the theory at present 

 suggested. 



I am not unaware of the difficulties in the way of its acceptance. The 

 colour of hsematin cannot, it is said, depend upon the iron it contains, 

 because nearly the whole of the iron may be removed without affecting 

 the colour of the haematin*. But it is not stated that all the iron is ever 

 removed, and it may be that a very small proportion suffices for the formation 

 of the colour, while the larger proportion of the metal is held in reserve in 

 the globules in the same manner as sulphocyanic acid appears to be in the 

 serum. 



Having found a sulphocyanide in the blood, it next occurred to me to 

 look for it in the eggs of birds. It is natural to suppose that, since in the 

 process of incubation red blood is formed, its assumed elements of colour 

 would be found in the egg before incubation. This supposition proved 

 correct. Fortunately the albumen of the hen's egg affords a ready means 

 of research. It is only necessary to mix it with an equal quantity of dis- 

 tilled water, by which complete coagulation by the iron solution is prevented. 

 The albumen of a lien's egg weighs about 300 grains, and this quantity was 

 found to contain ^ of a grain of sulphocyanic acid. The yolk was inti- 

 mately mixed with water, then evaporated to dryness in the water-bath, 

 and extracted with alcohol ; but no trace of the salt could be detected. It 

 is probable, therefore, that the sulphocyanide exists exclusively in the 

 * Elements of Chemistry. By W. Miller, M.D., 3rd edit. p. 872. 



