FORMATION OF CALLUS AFTER FRACTURE. 483 



developed in the same way or out of the same substance 

 (e. g. extravasated blood, periosteum, medullary tissue, 

 exuded fluids, etc.) has proved the greatest obstacle to 

 the true perception of the real state of things, and that 

 all have really had right upon their side, inasmuch as 

 new bone in fact builds itself up out of the most differ- 

 ent materials. Unquestionably, when the case runs a 

 very favourable course, that path is chosen in which the 

 new formation can be most conveniently effected, and 

 it is by far the most convenient way, when the peri- 

 osteum produces a very large portion of the whole. 

 This takes place in the following manner : the perios- 

 teum grows dense towards the edges of the fracture, 

 and there gradually swells' up, the swelling being of 

 such a nature, that separate layers or strata can after- 

 wards pretty clearly be distinguished in it. These 

 continually become thicker and more numerous, in con- 

 sequence of the constant proliferation of the innermost 

 parts of the periosteum and of the formation, by 

 means of a multiplication of their cellular elements, of 

 new layers, which accumulate between the bone and the 

 relatively still normal parts of the periosteum. These 

 layers may become cartilage, but it is not necessary, 

 nor yet the rule. For we find that, in the greater num- 

 ber of favourable cases of fracture, where cartilage is 

 produced, not the whole mass of the periosteal callus 

 is produced from cartilage, but a greater or less portion 

 of it is always formed out of connective tissue. The 

 layers of cartilage generally lie next to the bone, whilst 

 the farther we proceed outwards, the less does the for- 

 mation out of cartilage, and the more a direct transfor- 

 mation of connective tissue, prevail. 



The formation of bone is, however, by no means 

 restricted to the limits of the periosteum very com- 

 monly it extends beyond them in an outward direction, 



