INFARCTION 327 



nitrogen. Possibly some oxygen may also be released from solution 

 during decompression.-^ At body temperature fats can dissolve five 

 times as much nitrogen as serum or plasma,'^ which probably accounts 

 for the severity of the changes in the nervous system with its rich 

 lipoid content and delicate structure. Air embolism following obstet- 

 rical operations or surgical operations about the neck and chest pre- 

 sents chiefly mechanical features, ^^ and large quantities of air must be 

 present to cause dangerous obstruction to circulation. ^^ Gas-bubbles 

 may be produced in the blood soon after death by B. aerogenes cap- 

 sulatus, but it is not probable that they are formed before death 

 and cause air emboHsm. 



Infarction . 



The changes that occur in infarcted areas are of much interest in 

 connection with the study of autolysis, for the absorption of the ne- 

 crotic tissue of aseptic infarcts is purely a matter of autolj'sis. Ja- 

 coby-^ 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 leucine and tyrosine could be detected, just as they are 

 found in liver tissue undergoing autolysis 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 infarcts 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 al- 

 most exactly fourteen weeks old, there still remained a layer of ne- 

 crotic cortex one millimeter thick, quite unabsorbed during this time. 

 If we examine such aseptic infarcts in various stages, we get the im- 

 pression that the digestion is accomplished by leucocytes acting on the 

 peripher}^ of the infarct, and not entering the dead area deeply, pre- 

 sumably because of a lack of chemotactic substances in the dead cells. 

 On the other hand, it seems probable that the tissue enzymes them- 

 selves play an important part in the autolysis, for if we implant into 

 animals pieces of tissue in which the enzymes have been destroyed by 

 heating to boiling, it will be found that the cells and their nuclei re- 

 main unaffected for many weeks; whereas if sterile unheated pieces 

 of tissue in which the enzymes are still active are implanted, they lose 

 their nuclear stain and begin to disintegrate relatively soon, without 

 apparent participation by the leucocytes.-^ Ribbert-^ found that in 



21 HUl and Greenwood, Proc. Royal Soc. (B), 1907 (79), 284. 



"Vernon, ibid., p. 366; Quincke, Arch. exp. Path. u. Pharm., 1910 (62), -164. 



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



-^ See Hare, Anier. Jour. Med. Sciences, 1902 (124), 843. 



" Zeit. phvsiol. Chem., 1900 (30), 149. 



2« Wells, Jour. Med. Research, 1906 (15), 149. 



" Virchow's Arch., 1899 (155), 201. 



