140 ?• B. SIVICKIS. 



in sixths somewhat more, and in eighths still more, but in all cases 

 much less than in P. lata. Moreover, during the first twenty-four 

 hours after section it usually decreases almost or quite to the same 

 level as that of whole animals. In short, the presence of one or 

 even two cut surfaces has in itself little or no effect in increasing 

 susceptibility in P. dorotocephala. Differences in body level are 

 far more important, particularly in the shorter pieces. Even in 

 sixths or less the increase is slight in anterior pieces, becomes 

 greater toward the posterior end of the first zooid, and is again 

 slight in the posterior zooid. 



Evidently the increase in susceptibility in relation to cut surfaces 

 and the differential increase at different levels of the body depend, 

 at least in part, on different factors. The former, which seems to 

 be essentially a cellular wound reaction, followed by cell division 

 and growth, is the more conspicuous feature in P. lata. The dif- 

 ferential increase, on the other hand, is more conspicuous in P. 

 dorotocephala, but is present also in P. lata, and appears to be a 

 stimulation of the piece as a whole. Various facts, such as its 

 short duration and its inhibition by anesthetics (Buchanan, '22), 

 indicate that it is nervous in character. Moreover, it is of interest 

 to note that the differential increase varies inversely as suscepti- 

 bility at different levels of whole animals and inversely as head 

 frequency at different levels, while the increase in relation to cut 

 surfaces varies directly with area of cut surface in relation to size 

 of piece. 



Changes in Rate of C0 2 Production Follozving Section. — Colori- 

 metric estimations of C0 2 production confirm the data on sus- 

 ceptibility as indicative of changes in rate of respiration. In each 

 of these experiments five 12-13-mm. headless animals entire were 

 compared with five headless animals cut into eighths. The start- 

 ing point was pH 7.9, and the pH was recorded at regular inter- 

 vals, and the time required to reach pH 7.3 was also determined. 

 After the experiment both lots were weighed, and in all cases the 

 weight of the pieces was less by some 20 to 50 per cent, than the 

 weight of headless animals, because some loss of intestinal con- 

 tents, fluids, or even cells occurs when pieces are cut. In all cases, 

 however, the rate of decrease of pH of the pieces was equal to or 





