Embolism. 149 



the blood by a round-about way into one of the venae cavee. Clots 

 and fragments of clots from the capillaries and veins pass as 

 emboli to the right heart and thence to the lungs. 



In the same way as clots, a variety of substances may, if once 

 they have gained entrance to the blood, be carried along by the 

 current and give rise to embolism. Virchow and Cohnheim, whose 

 studies were fundamental to our kucnvledge of the embolic process, 

 showed that small balls of wax introduced into the blood vessels 

 are carried along by the current, lodge in some relatively narrower 

 place in the vascular tube, and give rise to all the mechanical con- 

 sequences of embolism. Sometimes parasitic worms which have 

 succeeded in making their way from the intestine into the radicles 

 of the portal vein are conveyed with the portal blood into the liver 

 and may be carried thence onward as emboli to the heart and lungs ; 

 very minute animal parasites, as the rounded oncospheres, measur- 

 ing only 20 to 40 micromillimeters in diameter, and larval tricliina", 

 may slip through the capillaries of the pulmonary circulation, often 

 measuring o.i mm. in diameter, and thus gaining access to the 

 arterial stream be carried to any of the organs. It may be easily 

 appreciated from this wliy the liver and lungs are the most 

 common sites for echinococcus cysts ; and the embolic mode of dis- 

 tribution of the parasites is recognized from their usual wide dis- 

 semination throughout the whole organ. Of the larger parasites 

 which the blood may aid in distributing, liver lUikes deserve special 

 mention ; these sometimes in their migrations in the hepatic par- 

 enchyma penetrate into the branches of the hepatic vein and may 

 pass with the blood through the right heart into the lungs. The 

 mechanical consequences of embolism by these animal parasites are 

 usually of little importance because of the minute size of the bodies 

 and the relative certainty of sufficient anastomotic supply to the 

 small areas affected ; and disturbances are only occasioned by 

 pressure, etc., in case the invading parasite increases in size. The 

 larger parasites like stroiii^ylus annatus are capable of directly 

 causing the same mechanical eft'ects as described iii connection 

 with blood clots (as cerebral embolism with infarction). 



The entrance of air and of dro])lets of fluid fat may also oc- 

 casion circulatory disturbances in a jnirely mechanical manner, in 

 the same way as blood clots. Air cuibolisui is of rare occurence 

 and is met with in operations on the neck." The air which is 

 drawn by the suction force of the lieart through a valvular venesec- 



*Traumatk- a^rrnmia was first observed in the horse l>y the French veterin- 

 arian, Verrier (1806). 



