132 REPORTS ON INVESTIGATIONS AND PROJECTS. 



live in the body-fluid of other related animals ; (3) ability to live in the body 

 of the host after the death of the latter; (4) resistance to high temperatures; 

 (5) resistance to COo; (6) resistance to HoS ; (7) resistance to decompos- 

 ing proteids ; and (8) resistance to acids and alkalies. The following results 

 were obtained : 



All of the forms experimented on can live for a certain length of time out- 

 side the body of Diadema, either in the body-fluid of the latter or in sea- 

 water. Form A lives in sea-water only 2 or 3 hours, D about 24 hours, C a 

 trifle longer, usually less than 30, while B lives for 2 or 3 days. The diflferent 

 forms therefore show considerable differences in their resisting powers, B 

 being about 24 times as resistant as A. 



The exclusion of air from a sea-water culture by boiling the water before 

 using it and keeping the culture in a tightly sealed dish has a favorable effect 

 on B, increasing its life to as much as a week, which is the longest period for 

 which any of the four forms have been kept alive in artificial cultures. A, C, 

 and D are scarcely affected one way or the other by this treatment. 



The body-fluid of Toxopneustes seems to be toxic to the parasites of Dia- 

 dema and vice versa. Placed in a few drops of Toxopneustes body-fluid, 

 form A from Diadema died in an hour and a half, B in 3 hours, and C was 

 living after 15 hours, but dead in 24. In the control culture in which the 

 same forms were kept in the body-fluid of Diadema, both B and C were alive 

 after 15 hours and B after 24. C therefore lives almost or quite as long in 

 the body-fluid of Toxopneustes as in that of Diadema, while B lives some- 

 thing less than one-eighth as long. Form D from Diadema unfortunately 

 was not available for this experiment. The same form from Toxopneustes 

 was killed by the body-fluid of Diadema in i to 2 hours. There are good 

 reasons for believing that mere differences in the concentration of the two 

 body-fluids can not account for the facts observed, but that chemical rather 

 than physical factors are involved. 



The four parasites behave differently after the death of the host. D dis- 

 appears as a rule in 12 to 15 hours, A in less than 20, and B and C often live 

 as much as 24 hours. None of the forms, however, have been found living 

 after 30 hours ; a diminution in the numbers of all can frequently be detected 

 in less than 12. 



A is killed by a temperature of 39.5° C, while B and C both succumb at 

 about 40.5°. Figures for D are not available. 



The forms in question show their most striking differences in their resist- 

 ance to chemicals. Experiments were made with a number of substances 

 which they either might be expected to encounter in nature (COo, HoS. de- 

 composing proteids), or which were at least representatives of a class of 

 such substances (HoSO^ and KOH as representatives of acids and alkalies). 



Placed in a gas-chamber filled with pure CO,, D is killed in 3 to 4 minutes, 

 A in 5 to 6, C in about 15, and B in 45 to 60. B is therefore about 15 times 

 as resistant as D. Water saturated with COo has a similar effect. 



Treated in the same way with HoS (which can be detected in the intestine 

 oi Diadema soon after death), C is killed in i to 2 minutes, D in about 3, A 

 in 3 to 4, and B in 10 to 15. B is therefore 8 to 10 times as resistant as C. 



Of an infusion made by allowing fragments of Diadema tissues to decay 

 in sea-water for 3 days, 5 drops were added to 10 drops of a culture con- 

 taining the four forms in question. B was killed almost instantly, certainly 

 in less than 5 seconds, A in 10 to 60 seconds, D in 20 to 25 minutes, and C 

 only after about 2 hours. C is therefore 1,500 times as resistant as B. 



