156 Papers from the Marine Biological Laboratory at Tortugas. 



EFFECT OF DECOMPOSITION PRODUCTS ON THE PARASITES. 



In an attempt to throw light on the cause of the disappearance of the 

 parasites after the death of the host, the effect on them of the direct products 

 of the decomposition of the tissues of Diadema was tried. The method 

 used was to allow fragments of Diadema tissues to decay in the water for 3 

 days at room temperature ; 5 drops of the resulting infusion were then added 

 to 10 drops of the fluid containing the animals. The results were most 

 surprising. B, which had hitherto proved the most resistant form in most 

 of the experiments, was killed almost instantly — certainly in less than 5 

 seconds; A lived from 10 to 60 seconds; Z) 20 to 25 minutes; and C as long 

 as 2 hours. C, therefore, which is less resistant than B to most conditions, 

 is in this case many more times resistant. The ratio for the four forms is 

 roughly 7:1: 1,500 : 250. These figures seemed so remarkable that the 

 experiment was repeated several times, but always with essentially the 

 same results. 



THE EFFECT OF H2SO4 ON THE PARASITES. 



A limited number of experiments were tried with this substance. It was 

 necessary first to determine the proper concentration, since if the solution 

 is too strong death occurs so quickly that its time can not be accurately 

 observed, and if too weak it occurs so late that other factors have time to 

 complicate the results. A series of preliminary experiments showed that a 

 favorable proportion is i drop of N/io H2SO4 to 5 drops of the fluid con- 

 taining the organisms. Of course, care had to be taken that the acid was 

 immediately mixed thoroughly with the culture medium, otherwise the 

 organisms were not all subjected to exactly the same conditions. Treated 

 in this way, the four forms showed striking differences: A had a very low 

 resistance, being killed in about 5 seconds; D was killed in less than 30 

 seconds, but the exact time (somewhere between this and 5 seconds) was 

 not noted; C died in about 30 seconds; while 5 survived 1.25 hours or 900 

 times as long as A . This is seen to be a surprisingly high resistance to acid 

 when it is remembered that Paramecium and many other fresh-water forms 

 are killed almost instantly by exposure to N/500 H2SO4. Summarizing the 

 results of the observations on the resistance of the four forms to H2SO4 we 

 have the ratio, i : 900 : 6 : < 6. 



EFFECT OF KOH ON THE PARASITES. 



This substance used in the same concentration as H2SO4, as might be 

 expected from results obtained with other animals, is on the whole much 

 less injurious. A (the least resistant form) was found to be killed in about 

 2 minutes, D in somewhat less than 45 minutes, B in about i hour, and C 

 in 3 to 4 hours. It will be noted that while A, C, and D are much more 

 resistant to KOH than to H2SO4, B is actually less resistant. The ratio for 

 the four forms is roughly i : 30 : 100 : 20. 



