16 BLOOU 



Although pus microbes are almost invaria,bly to be found in the collection 

 of pus formed under natural conditions, it is possible for pus to be produced 

 in the tissues by the introduction of chemical irritants (croton oil, for 

 instance), without the presence of pus microbes. This microbe-free pus 

 being composed of dead and inert matter, has no power to increase in 

 amount. Pus organisms are found abundantly in impure air, polluted 

 water, on skin and on mucous membranes, even when these two surfaces 

 are in the highest possible .state of health. If the action of the skin or 

 mucous membrane in protecting their respective underlying tissues be 

 weakened 'by injury, such as a wound, or even by slight inflammation, and 

 if pus microbes gain access to the part, the process of pus formation will 

 in all probability be set up ; supposing that these germs are sufficiently 

 numerous. If, however, they be few in number, they may be destroyed by 

 the cells of -the tissues taking them into their substance and digesting them. 

 The healthier the part, the greater power' will it have to resist an invasion 

 of these microbes. Thus we see that pus is formed under two conditions, 

 namely : injury sufficient to excite its production, and infection, for the 

 accomplishment of which, existing inflammation or an existing collection 

 of pus seems necessary. Pus organisms appear to gain access to deep- 

 seated tissues by means of the blood-stream ; probably, having been first 

 taken into the body through the air-passages or alimentary canal. As these 

 microbes have a destructive action on the tissues, and as their presence may 

 give rise to blood-poisoning (p. 516), our efforts should be directed to 

 prevent their invasion by aseptic treatment, and, if they have already 

 commenced it, to kill, or at least to render them inert before removal by 

 antiseptics. 



As a great rule, the leucocytes, as we have seen, proceed towards a part 

 which has been injured or into which some foreign body, such as a microbe, 

 has been introduced. The mechanical theory that the leucocytes move in 

 the line of least resistance, does not hold good in all cases ; for the presence 

 of certain substances, such as quinine and lactic acid, repels the advance' of 

 the leucocytes ; while other sulDstances, such as pure water and antipyrine, 

 neither attract nor repel. Almost all microbes exert an attractive influence 

 on the leucocytes. This theory of attraction is strengthened by the fact, 

 as' pointed out by Marcus Beck, that the flow of the exudation of inflam- 

 mation is away from the inflamed area, and that the migration of the 

 leucocytes is towards it. This subject has not as yet gone beyond the 

 bounds of theory. 



When inflammation, as in an ordinary sprain, for instance, is not followed 

 by the formation of pus, the exudation usually ceases within twenty-four 

 hours of the accident. New blood-vessels, soon begin to be pushed forward 

 from the ends of the divided surfaces into the coagulated fibrin which lies 

 between them, until they finally unite about the end of the first week. 

 Owing to the whiteness of our skins, we may by the red appearance of the 

 scar, readily note the presence of blood-vessels' in cuts which have been 

 recently inflicted on ourselves and which are healing in a favourable manner. 

 After about a fortnight, the new blood-vessels begin to diminish in size, and 

 altogether disappear in a few months. The scar-tissue gradually contracts, 

 and then becomes white and hard. It may in time degenerate and become 

 more or less absorbed. The process of repair follows the same lines, whether 

 the injury be a wound, sprain, or bruise, for example. 



It is instructive to note that the exudation in inflammation does not 

 repair an inflicted injury, which process is effected by the tissues. Further, 

 it seems that the presence of any portion of the exudation which remains 

 unabsorbed, say, for more than twenty-four hours, is actually hurtful, by 

 interfering with the local circulation, and by promoting the formation of 

 adhesions. Means, if possible, should therefore be taken to prevent its 

 occurrence, or ait least to hasten its removal. 



As the effectiveness of repair is inversely proportionate to the quantity of 

 scar-tissue employed in that process (compare the results, in wounds of 



