H2 AN INTRODUCTION TO SCIENCE 



dissolved in pure water, gives a clot. This brings the clotting 

 property home to the "globulins'* in the blood, since albu- 

 min is not precipitated by sodic sulphate. 



1861. Schmidt, remembering Buchanan's observations, 

 resolved to obtain Denis' "plasmine" as two separate glob- 

 ulins. He therefore repeated the experiment upon each of 

 the exuded lymphs, which clotted when mixed but would not 

 clot separately. He obtained two globulins which he named 

 "fibrinogen" and " fibrinoplastin," dissolved them sepa- 

 rately in water, and found that neither solution coagulated ; 

 but fibrin appeared when they were mixed. Proceeding, 

 however, to obtain them by another method in a purer state, 

 he found that his two globulins, when precipitated by a 

 stream of carbonic acid gas, would not cause a clot, either 

 when dissolved separately or when combined. However, 

 some of the washings of a blood-clot added to the mixture 

 caused it to coagulate. Schmidt therefore concluded that 

 three things are needed, fibrinogen, fibrinoplastin, and 

 "blood-ferment." But in drawing this conclusion he 

 neglected the indispensable scientific precaution to which we 

 have already called attention. He overlooked the necessity 

 for arranging a ' ' control experiment.' ' Hammersten showed 

 that Schmidt might have left fibrinoplastin out of the mixture. 

 When he precipitated it in a pure state he freed it from the 

 only essential constituent, the "ferment." Fibrinogen,///^ 

 ferment, yields a clot. Fibrinogen is dissolved in the plasma, 

 and does not become insoluble until it is acted upon by the 

 so-called ferment. The ferment is set free on the disintegra- 

 tion of the white blood-corpuscles (or of some other formed 

 constituent of the blood); and the reason for the delay in 

 coagulation which Hewson observed, when by ligaturing a 

 vein in two places he converted it into a bag of blood, is 

 that the corpuscles, when kept in a natural condition, retain 

 their vitality for a long time. With many blunders and much 

 following of false scents physiologists have gradually traced 

 the blood-clot to a soluble globulin, fibrinogen, which is 



