16 BLOOD. 



heakli. If the action of the skm or mucous membrane iu 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 conditionSj namely : injury sufficient to excite its production, and in- 

 fection, 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. 532), our efforts should be directed to jprevent 

 their invasion and, if they have already commenced it, to kill, or at least to 

 render them inert before removal. 



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, repel the advance of the 

 leucocytes ; while other substances, 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 inflammation 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 (Billroth). 

 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 efl'ected 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 at least to 

 hasten its removal. 



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

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

 healing by immediate union with those by granulations) ; we should abstain 

 from ajjplying stimulants (such as blisters, embrocations, and the hot iron) 

 to the seat of injury, until we feel certain that the new vessels in the scar- 

 tissue have become entirely obliterated. 



Muscular wasting is frequently seen in the muscles of parts which have been 

 the scat of inflammation, as in sprain of the shoulder (p. 60) and fracture of the 

 pelvis (p. 305). In the former, the muscles covering the shoulder-blade 

 waste ; in the latter, those of the croup suffer from atrophy. Disuse is the 

 cause generally assigned to decrease of substance. I am inclined to think 

 that the presence of inflammation, by interfering with the circulation of the 



