The Physiology of Nematocysts 363 



10 gr. flaked pepsin. The digestive processes took place quite 

 rapidly, in some instances being complete within 24 hours. The 

 solutions were then centrifugated, and there was obtained a thick 

 sediment, composed, in the case of Physalia especially, of count- 

 less isolated, undischarged nematocysts. Many discharged ones 

 also were found, but these formed a minority. The same meth- 

 ods were employed in the case of the auto-digestion. 



Experiments to be described later, showed that although these 

 methods are adequate, the nematocysts are changed in certain 

 ways by these processes, and we therefore resorted to the maceration 

 method referred to. For this purpose the acontial filaments of 

 Metridium were found extremely good as they are composed of 

 immense numbers of nematocysts held together by a minimum of 

 other tissues. In sea-water to which crystals of chloretone are 

 added slowly from time to rime for a period of about 12 hours, the 

 acontia break down, forming a somewhat glutinous mixture in 

 which free undischarged nematocysts occur in great abundance. 

 These were in excellent condition for some of the purposes for 

 which we used them. 



In order to store nematocysts for later use, and this was neces- 

 sary as we secured only one specimen of Physalia, and that early in 

 the summer, we dessicated some of the sediment secured from the 

 centrifuge, preserved some in glycerine, some in sea-water, and 

 some in salt solutions of various concentrations. Under these 

 circumstances the material keeps perfectly well, and can later be 

 used for experimental work. 



During the course of the experiments carried out at Wood's Hole 

 it became desirable on several occasions to separate the discharged 

 from the undischarged nematocysts, and also to isolate individual 

 capsules. The former was accomplished in two ways, sometimes 

 by means of what might be called a "capillary filter," the dis- 

 charged nematocysts failing to be drawn up into a capillary tube 

 just large enough to admit undischarged ones; sometimes by 

 taking advantage of the somewhat lighter specific gravity of the 

 exploded capsules. In a dish containing both discharged and 

 undischarged nematocysts, the former come to lie above the latter 

 and may be completely removed by means of a small glass hook. 



