256 



the tail, and afterwards pricking the portion of this organ 

 retained in connection with the hody with a fine needle, or 

 passing- over it a firm brush furnished with fine hairs. 



Simple excision of the tip of the tail in most instances led 

 to no good resvilt, since, except in a small sore lying at the 

 margin of the wound, in which stasis and extravasation had 

 been produced, no changes could be observed. In like 

 manner, puncture of the tail in relatively few instances only 

 was attended with any success ; stasis and extravasation were 

 similarly established, and so prevented examination. On the 

 other hand, the application of the small brush after excision 

 of the tail proved very successful. 



By an occasional application of water to the whole of the 

 creature the tadpole was kept moist. From time to time, 

 usually at intervals of from one half to one quarter of an hour, 

 the application of the brush was renewed. 



Immediately after the application of the irritant masses of 

 colourless blood-corpuscles accumulate in some of the vessels 

 near the injured part, and through the walls of the vessels 

 several of the corpuscles may be seen to make their way. 

 There are presented to observation near the vessels cellular 

 elements, which, although branched, differ very much from 

 the branched cells situated at a distance from the injured 

 vessels, or in unirritated portions of the tail. These are not, 

 as in the normal condition, marked by sharp angles, nor are 

 they so smooth and large, but appear contracted and studded 

 with small prominences, from Avhich processes are given off. 

 Moreover, they are considerably smaller, and are often drawn 

 together so as to form a small rounded lump which sends 

 forth on all sides long single or branched processes. 



One may best attain conviction concerning these changes 

 by delineating, before the application of the irritant, at a 

 readily accessible spot, several branched cells lying near 

 vessels. The tail may be then bruslied, and observation again 

 directed to the spots in question. 



When the irritation is slight the cells will soon regain 

 their previous normal form ; they again become smooth, 

 acquire their sharj) angles, from which processes set out. With 

 a sufficiently strong stimulus, however, further clianges in 

 form supervene on the above-mentioned alterations ; at one 

 spot a prominence is extruded, which is gradually elongated 

 into a process, or the body of the cell becomes acuminate at 

 one spot, and a process extruded at this point; the extruded 

 processes are afterwards slowly withdrawn, whilst at other 

 spots similar processes are again put out. During these 

 occurrences the cell mass also changes its form. 



