84 PROTOZOA AND DISEASE 



What causes Granulation Tissue to form ? It is worth while to 

 ponder a moment to inquire what the immediate causes of this 

 awakening of the connective-tissue cells into active life may be. 

 The outpoured blood and lymph afford them an abnormally abundant 

 supply of food ; and in all probability it is this factor that determines 

 the increase in size and activity of the cells. In repair of rabbits' 

 tendons, as stated above, I was unable to find any evidence of cell 

 reproduction other than by indirect division. Cell multiplication 

 by the simpler process of direct nuclear division may occur when 

 the normal conditions are altered to a less extent ; for example, 

 when there is accumulation of lymph about the cells of fibrous 

 tissue, or, in other words, oedema of a part, the supply of food 

 to the cells will not be so abundant as when coagulable plasma 

 escapes with blood from divided vessels, and yet it may be sufficient 

 to cause multiplication of the connective-tissue cells. Such an 

 oedema of the surrounding fibrous tissues will occur where any 

 tumour is growing in the body of any animal. The increased 

 tension exercised by the tumour on the surrounding parts must take 

 effect upon the veins and lymphatics, in which pressure is low or 

 negative, before it tells upon the arteries, in which there is a positive 

 pressure. As a result, there must be around a growing tumour a 

 zone of oedema, which may increase the nourishment of the fibre - 

 blasts sufficiently to cause them to increase in numbers and form 

 granulation tissue. To these changes may be added strictly inflam- 

 matory ones due to toxic materials, which cause changes in the 

 walls of the bloodvessels and attraction or repulsion of leucocytes 

 (chemiotaxis). 



Nuclear Changes in the Cells of Granulation Tissue. In normal 

 connective tissue the nuclei of the cells of the bundles of fibres lie 

 flattened and curved to fit the contour of the bundles. They are 

 very poor in chromatin. When the fibrous bundles become 

 separated by an unusual amount of lymph, the nuclei fill out, 

 assuming ovoid or spherical forms, and, if the condition of oedema 

 persists, the chromatin becomes more abundant, and preparations 

 for cell-division begin. 



