INFARCTION 273 



that of the atmosphere (diver's palsy, caisson disease, etc.). This 

 form of air embolism is due to the fact that fluids can dissolve 

 much more gas at high pressures than at low pressures ; con- 

 sequently when the abnormally great pressure to which divers, 

 caisson workers, etc., are subjected is too suddenly reduced to 

 that of the atmosphere, the excessive gas that was absorbed 

 during the period of high pressure by the blood and tissue 

 fluids is released, and forms bubbles in the tissues and blood. 

 The bubbles in the nervous tissues may cause paralyses of vari- 

 ous sorts, or death ; those in the blood may, if in sufficient 

 amount, cause serious or fatal capillary obstruction. The bub- 

 bles consist chiefly of nitrogen, because the power of the blood 

 to hold oxygen in combination is so great that not much of this 

 gas becomes freed. 1 Air embolism following obstetrical oper- 

 ations or surgical operations about the neck and chest presents 

 chiefly mechanical features, 2 and large quantities of air must be 

 present to cause dangerous obstruction to circulation. 3 Gas- 

 bubbles may be produced in the blood soon after death by B. 

 aerogenes capsulatus, but it is not probable that they are formed 

 before death and cause air embolism. 



INFARCTION 



The changes that occur in infarcted areas are of much interest 

 in connection with the study of autolysis, for the absorption of 

 the necrotic tissue of aseptic infarcts is purely a matter of autol- 

 ysis. Jacoby 4 found by ligating off a portion of a dog's liver, 

 and keeping the dog alive for some time afterward, that in the 

 infarcted tissues so produced leucin and tyrosin could be 

 detected, just as they are found in liver tissue undergoing autol- 

 ysis outside of the body. So, too, proteoses may appear in the 

 urine when any considerable amount of tissue is cut off from 

 its blood-supply. The processes of autolysis which occur in 

 ordinary sterile iufarcts are, however, extremely slow, and it is 

 doubtful if enough of the products are ever in the blood or 

 urine at any one time to be detected or to cause noticeable 

 effects. For example, in an infarct of the kidney which was 

 known to be almost exactly fourteen weeks old, there still 

 remained a layer of necrotic cortex one millimeter thick, quite 

 unabsorbed during this time. If we examine such aseptic 



1 This subject is fully discussed by Leonard Hill in "Recent Advances 

 in Physiology and Biochemistry," London, 1906. 



2 Review of literature by Wolff, Virchow's Archiv, 1903 (174), 454. 



3 See Hare, Amer. Jour. Med. Sciences, 1902 (124), 843. 

 *Zeit. physiol. Chem., 1900 (30), 149. 



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