PiniiOIIS TISSUK I'UODUUKD AS A K'KAC/rioN TO IN.TIIK'Y. 601 



tioiij travelling in all directions between the muscle-fibres. 

 On reaching the gill-tissue the corpuscles come to rest, and 

 form a dense, agglutinated, plasmodial mass, completely sur- 

 rounding and shutting off the gill-tissue from the neighbour- 

 ing muscle (fig. 1). They soon appear as if they had under- 

 gone some degree of pi-essure and the nuclei are slightly 

 flattened, probably owing to the contraction of the plasmodial 

 nuiss as it tightens round the implanted gill-tissue (Drew, 4). 

 In time the corpuscles show signs of degeneration ; the 

 nuclei become irregular in outline, and the chromatin is 

 represented by numerous gi^anules staining darkly with 

 ha3matoxylin. The degenerated mass of corpuscles is then 

 invaded by fresh blood-cells, and is more or less conipletely 

 removed, apparently partly by a process of phagocytosis and 

 partly by autolysis. 



While this is going on, the cells of the gill-filaments have 

 degenerated, their outlines are ill-defined, and the nuclei no 

 longer discernible; the bacteria present multiply consider- 

 ably. 



The degenerated gill-tissue is then invaded by blood-cor- 

 puscles which have penetrated through the surrounding mass 

 of agglutinated cells, and in most cases the bacteria and 

 epithelial debris are removed by phagocytosis, leaving only 

 the chitinous supporting-rods of the gills. 



In the course of this pi-ocess many of the invading cells 

 also are destroyed, and appear in their turn to be removed by 

 oilier phagocytes. In time the whole space originally occupied 

 by the gill-tissue becomes filled with a loosely packed nuiss 

 ot blood-cells, among which the chitinous supporting bars are 

 the only relics of the original implanted mass. In many of 

 our experiments bacteria multiplied so rapidly that the phago- 

 cytes were unable to cope with them. Consequently the 

 bacteria invaded the neighbouring tissues, entered the blood- 

 spaces, and rapidly caused death. 



In preparations from obviously unhealthy animals, it was 

 commonly found that the bacteria had penetrated beyond the 

 protecting mass of agglutinated cells and had invaded the 



