LANCASHIRE VETERINARY MEDICAL ASSOCIATION. 
355 
as dead bone or slough, is present, the irritation of the granulation tissue 
of the pyogenic membrane is kept up principally by the tension of its 
contents. Of this we have proof by the physical signs and the pain of 
which the animal gives evidence. The young cells exert a disintegrating 
action on surrounding structures following the direction of least resist¬ 
ance until the abscess “ points 55 at some free surface. Poultices and 
other forms of moist heat favour the dissolution of the textures by ren¬ 
dering them more permeable to fluids. Antiseptic surgery, by its results, 
has shown that when such a collection of pus is laid freely open and the 
tension removed, the granulations of the pyogenic membrane behave 
as do those of the ordinary healthy healing wound to which I have 
directed your attention. That is to say, where the sac-like pyogenic 
membrane is opened out its purulent discharge gets free vent, and it is 
reduced, somewhat imperfectly, to the condition of an ordinary granu¬ 
lating surface, as in a healthy ulcer. 
The opening of an abscess removes the irritation produced by tension, 
and if external irritating conditions be kept out, as by appropriate anti¬ 
septic dressings, granulations have been seen to grow without the 
production of an atom of pus. So far, the cells of granulation tissue 
have been conclusively shown to be derived from emigrated blood- 
corpuscles and proliferated tissue-cells. The relation of granulation 
tissue to the healing of wounds and the secretion of pus, together with 
the modifying influence exerted by irritation on pus formation has been 
established. 
A question now arises : Is pus the only product of granulation tissue ? * 
Granulation tissue grows ; and suppose the process of growth went on we 
should find a fleshy tumour, consisting of small round cells like white 
blood-corpuscles, with little intercellular substance; in fact, we have in 
granulation tissue an identity in structure with what is known as a round- 
celled sarcoma. It is needless for me to draw your attention to the fact 
that these round cells of granulation tissue are of the same structure as 
the embryonic cells, from which all tissues are primarily developed. In 
the diagram No. 9 these young spherical cells are represented in a healing 
sore, and at the right hand corner you observe coloured yellow a forma¬ 
tion of cuticle or epidermis; deeper you notice some of the cells of the 
tissue become spindle shaped, and develop into fibrous tissue ; simulta¬ 
neously with these changes the secretion of pus commences to disappear. 
At the right hand corner the cuticular formation is represented. 
Why does epidermis in places where the skin has been wholly destroyed 
form only at the edges ? This has been a tedious problem to most 
observers. The fact that a successful graft leads to an island of develop¬ 
ing epidermis is capable of two explanations. The newly-planted 
epidermic cells, like those at the edges of the wound, may themselves 
proliferate, and develop a progeny of scales by their multiplication, or, 
to speak more definitely, epithelial scales arise by multiplication of 
previously existing epithelial cells. The second interpretation suggests 
that the young cells of the granulation tissue are influenced by the nature 
of the surrounding texture. The skin graft acts, we may say, as a 
decoy, leading the young cells of the granulation tissue to develop like 
unto it into epidermic scales of the cicatrix. Similarly, the deeper con¬ 
nective-tissue elements may be looked upon as exerting the influence of 
their presence on the deeper cells leading to the development of them 
into connective tissue. 
It is extremely interesting to find that granulation cells, formed to 
repair a breach of osseous tissue, such as after fracture, necrosis, or 
abscess, develop into bone. In the development of granulation cells into 
