384 THE BLOOD AND THE BLOOD-FORMING ORGANS. 



In many cases of injury, particularly in crushing fractures of the 

 bone, the fat of the marrow finds its way into the blood, and it may col- 

 lect in large drops in the vessels of the lungs, forming the so-called fat 

 emboli (Fig. 13, p. 75) ; or it may pass the lungs and form emboli in 

 other parts, as the brain, kidneys, etc. Fat embolism in eclampsia is of 

 occasional occurrence. 



The fat may be absorbed from the vessels, having produced little or 

 no disturbance ; or in some cases it may produce serious results by the 

 stoppage of a large series of vessels in the lungs, brain, or other parts of 

 the body. ' 



Tissues and organs whose blood-vessels are suspected to contain fat droplets should 

 be fixed with osmic acid, which stains fat black. Sections without further staining 

 may be mounted in glycerin. 



Air, as a result of an opening in the veins, is of occasional occurrence. 

 If the amount of air be small, it appears to be readily absorbed, and does 

 little or no harm. If, on the other hand, a large quantity is admitted to 

 the veins at once, it collects in the right side of the heart, from which 

 the contractions of the organ are unable to force it in any considerable 

 quantity, and, the supply of blood being thus cut off from the lungs, 

 death very quickly ensues. The blocking of the smaller pulmonary ves- 

 sels and of the vessels of the heart with air bubbles may also hasten 

 death. It is especially from wounds of the veins of the neck and thorax 

 that the accident is most apt to occur. But it may be due to the intro- 

 duction of air into the uterine veins in intra-uterine injection, or in the 

 removal of tumors. 2 One should remember in this connection that in- 

 fection with bacillus aerogenes gives rise to gas bubbles in the blood-ves- 

 sels, as well as in other tissues (see page 267). 



Parasites and Other Foreign Bodies in the Blood. The occurrence of 

 animal and vegetable parasites is considered more in detail in parts of 

 this book devoted to these organisms. It will suffice to mention here 

 that the more important of the animal parasites of the blood are : The 

 malarial parasite, trypanosomata, and Filaria sanguinis hominis. 



The various forms of bacteria which may be found in the blood will 

 be considered in parts of this book in which these organisms are treated 

 in detail. 3 Parenchyma -cell emboli are considered on page 76. 



1 For resume of this subject with bibliography, consult Welch in article on Embol- 

 ism in Allbutt's "System of Medicine," vol. vi., p. 258. 



* Welch, ibid., p. 254. 



3 For methods and results of bacterial studies of the blood, with bibliography, con- 

 sult Kuhnau, Zeit. f. Hygiene, Ed. xxv., p. 492, 1897; liosenberger, Am. Jour. Med. 

 Sciences, 1903, p. 234. ' 



