BACTERIA. 63 



METHODS OF REPAIR. — For practical purposes, we may adopt Paget's 

 classilication, which is as follows: (1.) Immediate union. Here, the parts 

 behig brought into exact contact, unite in a few hours, without any per- 

 ceptible material being deposited between them ; hence there is no vii-ible 

 scar. To obtain this result, which, would be rarely possible in horses, the 

 intiammation must have been very slight. (2.) Union by primary adhesion. 

 In this, the divided surfaces are glazed over by a fluid which is exuded from 

 them, or by the coagulation of a thin film of blood, either one, or both, of 

 which substances may form in two or three days a temporary means of union, 

 which material, as explained by Hamilton, will have to be absorbed before 

 permanent union, which will leave a scar, can take place. In fact, the 

 greater the quantity of this temporary adhesive material, the longer will the 

 wound take to heal. (3.) Granulation. This is a tedious process which is 

 invariably accompanied by the formation of pus, and is the one by which, as 

 a rule, all wounds, except clean-cut ones, heal. (4.) Union of granulating 

 surfaces. (5.) Healing under a scab. "All wounds heal in essentially the 

 same manner, namely, by the growth and organisation of new tissue from 

 corresponding old tissues already present in the part. The whole process is, 

 strictly speaking, one of growth followed by organisation, and any dift'erences 

 which" wounds present in bringing this to a successful issue are merely super- 

 ficial " {Hamilton). 



BACTERIA AND DISEASE GERMS.— Soil, water, and to a less extent 

 air are filled with microscopic germs (bacteiia) whose function is to set up 

 decomposition in animal and vegetable matter that is in a fit condition for 

 this change. Some of these germs (those of pus) cause putrefaction ; and 

 others, respectively, give rise to special diseases, such as tetanus, and various 

 kinds of fever. Putrefactive germs are always present. The microbes of 

 special diseases are only occasional visitors, or their numbers are usually too 

 few to injuriously affect the system. In health, the skin and mucous mem- 

 brane protect the bod}^ more or less efficiently from the action of bacteria. 

 When either of these coverings become injured, as in the case of a wound or 

 bruise, the underlying tissues are rendered specially liable to an attack of 

 these germs, which fact is shown by the tendency that the seat of hurt has, 

 in these cases, to form " matter " (pus) ; in other words, to suppurate. I 

 have already explained that ordinary pus, like gastric juice, has the power 

 of dissolving the tissues. Hence its unchecked presence in a part is 

 characterised by the formation of matter resulting from tissue destruction. 

 This diseased product (pus) may appear as a discharge from a wound, or as 

 a collection of fluid in an abscess. The skin which covers an abscess becomes 

 thin and weak, owing to the corroding action of the contained pus (p. 15) ; the 

 usual result being that the abscess, if circumscribed in a sac, will in time tend 

 to " point." 



Contrary to what we might suppose, living tissues and blood do not 

 form a particularly suitable place of residence for putrefactive and disease 

 germs, especially if these microbes, as in ordinary air, are comparatively few 

 in number. Also, the tissues have the power of resisting, to a certain extent, 

 their inroad, and even of destroying them. Thus, the liability of a wound to 

 infection, is influenced by the number of the germs, and by the resistance 

 (or health) of the part. From these considerations and from experience we 

 see that clean cut wounds which are exposed only to ordinary fresh air, will 

 continue healthy for a far longer time than those which have become tainted 

 with dirt and especially with decomposing matter, in which, bacteria teem. 

 Impure air, particularly, when loaded with du^t, has highly infective 

 properties ; and water which is fit for drinking has only feebly infective 

 power. A most important point to remember is, that moisture favours the 

 development and multiplication of bacteria; hence the drier a wound is kept, 

 the better will it resist their attack. I may add as an illustration bearing on 

 this subject, that the more concentrated meat soup is, the longer will it keep 

 fresh. The presence of bacteria in a wound is objectionable ; because, as I 



