370 PROTEIN-COMPOUNDS. 



body/ 5 ) the constituents of the ash unfortunately afford very 

 little information regarding the actual constitution of the salts that 

 existed previously to the calcination of the residue. 1 must more- 

 over remark, that the boiling must be continued for some time, in 

 order that the acid reaction after the coagulation of the globulin 

 may manifest itself. 



Preparation. As in the case of soluble albumen, it is impos- 

 sible to prepare soluble globulin in a perfectly pure state. Globulin 

 presenting the reactions which we have already indicated, may be 

 obtained by neutralising with acetic acid the fluid of the crystalline 

 lens, evaporating it to dryness at a temperature not exceeding 50, 

 and extracting the residue with ether and dilute alcohol. The 

 globulin of the blood, which cannot be separated without decom- 

 position of the hsematin, presents, with the exception of its colour, 

 exactly the same relations as the globulin obtained in the above 

 manner from the crystalline lens. 



Mulder prepared coagulated globulin by simply extracting with 

 alcohol and ether globulin which had been precipitated by boiling. 

 The coagulated globulin which I examined was precipitated with 

 hydrochloric acid, washed with the same acid, then dissolved in 

 water, again precipitated by carbonate of ammonia, and finally 

 washed with water, alcohol, and ether, after which it left no per- 

 ceptible ash. 



Tests. In the preceding remarks we have mentioned the 

 reactions by which globulin may be distinguished from the similar 

 protein-compounds : we will here merely add that no other soluble 

 protein-compound is precipitated both from its acid and its alkaline 

 solution by neutralisation, although almost all the insoluble 

 protein-compounds possess this property a circumstance which 

 affords a proof that globulin is reduced to the coagulated state both 

 by an excess of alkali and by an excess of acid. In our observa- 

 tions on casein, we shall point out how it may always be distin- 

 guished from that substance. It will always be difficult indeed 

 at present it is impossible to recognise globulin with certainty 

 when it is mixed with albumen or casein. Here, unfortunately, 

 elementary analysis affords us no assistance, since it so closely 

 approximates in its ultimate constitution to other protein-com- 

 pounds. 



In attempting a quantitative determination of globulin we must 

 adopt the same precautionary measures as in the determination of 

 albumen 5 indeed, as we have already shown, there are even greater 



