1 8 M. H. JACOBS. 



was also made apparent by the cessation of all movements of the 

 contractile vacuoles. Swimming, however, continued, though at a 

 slower rate than before. 



All of the effects so far described were found to be completely 

 reversible. Even after the protoplasm had passed through its 

 period of liquefaction and had become much more solid than at the 

 beginning of the experiment the animals practically all recovered 

 normally when the CO 2 was allowed to escape. From 56 minutes 

 onward, however, evidences of fatal injury began to appear. The 

 animals exposed for this length of time showed a mortality of 

 about 25 per cent., though those that did not die recovered entirely 

 normally. By the end of 65 minutes the mortality had increased 

 to approximately 75 per cent., and 10 minutes later to 100 per cent. 

 Since solidification began to be evident in some individuals in 25 

 minutes and was present in nearly all in 40 minutes, and since 

 scarcely any deaths occurred before 50 minutes, it is evident that 

 there is a considerable period within which the solidification is 

 completely reversible. With an exposure of longer duration, how- 

 ever, it apparently merges imperceptibly into an irreversible death 

 coagulation. 



The effects so far described are much more rapidly produced if 

 the animals have been kept in distilled water for a time before 

 their exposure to carbon dioxide. For example, in one experiment 

 a certain degree of liquefaction was produced in animals in the 

 normal culture medium in 12 minutes ; in individuals from the same 

 culture which had previously been washed in distilled water this 

 point was reached in less than 6 minutes. The times for the be- 

 ginning of solidification in the two cases were 40 and 12 minutes, 

 respectively, and while the animals in the culture medium were still 

 living at the end of 60 minutes, those in the distilled water were 

 dead in 32. These differences are perhaps partly due to the greater 

 hydrogen-ion concentration of the distilled water, but experiments 

 that need not be described here have shown that this is not the only 

 factor concerned. The situation is, in fact, a complex one, pre- 

 senting a number of points of interest, and its fuller discussion in 

 another paper is contemplated. 



At this point it may perhaps be well to consider two questions 



