COAGULATION OF BLOOD 



195 



salt solution and pass a stream of carbon dioxide through it. Clotting is not 

 produced as it is in ' peptone ' blood (which see). In order to produce clot- 

 ting, excess of serum, or some fluid containing thrombin must be added. 

 The action of leech extract is mainly due to the fact that it contains anti- 

 thrombin. 



(<?) The experiments described under d may be repeated with leech 

 extract plasma, obtained from the blood by centrifugalising. 



(/) Instead of leech extract, a solution of its active principle (hirudin) 

 may be used. This produces no fall of blood pressure, and so contrasts 



FIK. uo. Centrifugal machine as made by Kunne. Glass vessels containing the substances to be 

 centrifugalised a;e placed within the six metallic tubes which hang vertically while the disc is at 

 rest ; when the machinery is set going they fly out into the horizontal position. 



with what occurs in ' peptone ' injection. Leech extract produces a very 

 small fall of arterial pressure. 



o. Influence of Commercial Peptones (Proteoses) on Coagulation. For the 

 purpose of the following experiments another dog must be employed. 



The animal having been anaesthetised a cannula is placed in the 

 external jugular vein for the injection of the 'peptone.' 



The carotid artery is connected to a mercurial manometer for the 

 registration of arterial pressure. 



Another convenient artery must be exposed and a cannula inserted into 

 it for the collection of samples of blood. 



(a) First draw off a sample of blood and note its coagulation time. 



(6) Draw a second sample into a strong solution of commercial peptone. 

 The coagulation time is somewhat longer than in a. 



(c) Then inject the peptone quickly, so that the animal receives 0'3 

 gramme per kilo, of body-weight. Note during and for some time after the 

 injection a great fall in arterial blood pressure. This has been shown by 

 the oiicometer to be due to vascular dilatation. 



o 2 



