586 



inflamed part behaves itself in the same way as when separated 

 from the living body, naturally leads us to infer that the tissues of 

 the inflamed part are in some degree approximated to the condition 

 of dead matter, or, in other words, have suffered a diminution of 

 power to discharge the offices peculiar to them as components of the 

 healthy animal frame. This inference is strongly supported by 

 considering what common effect is likely to be produced upon the 

 tissues of the frog's web by all the various agents known to cause 

 inflammatory disturbance of the circulation." It is then pointed out 

 that all these agents, though differing greatly in their nature, agree 

 in their tendency to inflict a lesion on the part to which they are 

 applied, and impair the functional activity of the tissues. " But 

 strong as are the arguments thus obtained by inference, it would 

 be very desirable to confirm them by direct observation of the 

 tissues. It fortunately happens that the pigmentary system of the 

 frog is a tissue which, from its peculiar form and colour, is very 

 apparent to the eye, so that it is easy to trace the remarkably active 

 functions with which it is endowed, and their modifications under 

 the influence of irritation." 



The author then mentions the circumstances which led him to 

 notice that the dark pigment of the frog presents remarkable differ- 

 ences of appearance at different times in one and the same animal ; 

 each dark patch being sometimes of stellate figure with minutely 

 ramifying rays, at other times in the form of a small rounded spot. 

 These changes had been before observed by some German writers, 

 who attributed the rounded form to contraction of the branching 

 rays of a stellate cell. This, however, the author finds to be erroneous, 

 and in a supplementary section " on the anatomy and physiology of 

 the pigmentary system of the frog," shows that the cells never change 

 in form or size, but that the pigment-granules which are suspended 

 in a colourless fluid are capable of being, on the one hand, attracted 

 by a central force into a small space in the body of the cell, and, on 

 the other hand, dispersed by a repulsive power into the minutest 

 recesses of the ramifying rays. Both concentration and diffusion of 

 the pigment may take place with great rapidity, implying remark- 

 able energy in the attractive and repulsive forces, both of which 

 appear to reside in a nucleus. The supplementary section concludes 

 with some remarks on the physiological importance of the actual 



