457 



then the ampullar systole. The length of the pulsations when assisted 

 by the action of the heart, and when opposed by it were compared; 

 the eflFect of gravity acting against and with the contractions of the 

 ampullae at the end of a long blood vessel was tested. One half of a 

 colony was also subjected to pressure, thus forcing part of the blood it 

 contained into the other half and the influence of this increased blood 

 supply upon the rythm of the ampullar pulsations was examined. The 

 results of these experiments indicated that increased pressure slightly 

 lengthened the systole; but the changes noticed were so small that 

 they fell within the normal variations of the pulsations, and thus 

 cannot be considered as establishing the influence of a change of blood 

 pressure upon the ampullar contractions. 



The extent of the contractions like their rapidity is small. In 



Fig. 1. A normal ampulla, contracting a little 

 more vigorously than is usual. The continuous 

 line shows its shape at the beginning of the sy- 

 stole and the broken line at its end. Camera, 

 xS6. 



Fig. 2. A small group of ampullae one day after 

 isolation from the rest of the yascular system, 

 showing the alternate nature of the contractions. 

 The continuous line shows the outline of the 

 whole group before the lower ampulla has con- 

 tracted, and the dotted line after it has contrac- 

 ted. It will be seen that when one end is con- 

 tracted the other is expanded. Camera, x 86. 



many cases the change in shape may be detected by simple inspection, 

 but often an ocular micrometer or a camera drawing is necessary to 

 make sure that a contraction actually occurs. But although the motions 

 of the ampullar walls may be hard to detect, the movements of the 

 blood corpuscles are very evident, and it was by means of them that 

 the data for the ampullae in tables 3 and 4 were obtained. Figures I 

 and 2 show the extent of the contraction, the latter especially showing 

 that the contraction may take place in all directions, decreasing the 

 length as well as the diameter of the ampullae. The small extent and 

 extreme slowness of the contraction, and the fact that it is not always 

 limited to one direction agree well with the simple structure of the 

 contracting tissue, which is a thin pavement epithelium without any 

 fibrous differentiations that I have been able to detect. 



