Physiological Studies on Certain Protozoan Parasites. 153 



visibly injured. If, however, a few cubic centimeters of the mixture be 

 placed in a covered glass dish which prevents evaporation but which, being 

 only partially filled, does not prevent contact of the liquid with the air, it 

 will be seen that all of the animals present will die after a length of time 

 which is fairly constant for each species. The first one to disappear appar- 

 ently always is A , which is no longer present after 2 to 3 hours. 



It may be mentioned that no way of keeping A longer than this in arti- 

 ficial cultures was found except to place a relatively large quantity of the 

 intestinal contents in a test-tube with the addition of only sufficient water 

 to keep it moist, in which case the animals retained their activity somewhat 

 longer. D is next to A in respect to its behavior in sea-water culture, and 

 usually is dead at the end of 24 hours, though a few individuals may survive 

 several hours longer. C does not differ very markedly from D, but is some- 

 what more resistant, living on an average 30 hours or a little over. B is 

 by far the most resistant form, often surviving and continuing active for 

 2 or 3 days. The relative ability of the four forms to live outside the body 

 of their host may therefore roughly be expressed by the ratio i : 24 ': 12 : 10. 



To determine to what extent the injurious effects of removing the para- 

 site from their host were due to the action on them of the oxygen of the air, 

 a parallel series of experiments was tried in which oxygen, so far as possible, 

 was excluded. This was done by shaking up the food pellets from the 

 intestine with sea-water from which the air had been removed by boiling 

 (the concentration of salts being kept constant by the addition of distilled 

 water) and immediately placing the liquid in dishes which were completely 

 filled, covered, and sealed with vaseline to exclude the air. Such treatment 

 was found not materially to alter the length of life of any of the forms except 

 B, which in one such experiment lived for 7 days, the longest time for which 

 it was found possible to keep any of the forms alive by any of the methods 

 employed. A, C, and D died in about the usual times, the life of ^, if 

 anything, being slightly shortened and that of C slightly lengthened. In no 

 case except that of C, however, were the differences significant. 



ABILITY OF THE PARASITES TO LIVE IN THE BODY-FLUID OF TOXOPNEUSTES. 



Early in the course of these experiments it was observed that the forms 

 in question live in cultures made with the body-fluid of Diadema about the 

 same length of time that they do in sea-water. This is not surprising, since 

 the osmotic properties of the body-fluids of sea-urchins and sea-water are 

 about the same. A point of some interest seemed to be whether the body- 

 fluid of a nearly related genus of sea-urchins would be as favorable as that 

 of the host or as sea-water, or whether there might be present in it in addi- 

 tion to the salts of sea-water certain other substances of more specific 

 nature which would have a toxic effect. To determine this point, therefore, 

 experiments were made, but unfortunately they were not very extensive. 

 One such experiment may be mentioned. A, B, and C obtained from 

 Diadema were placed in a small quantity of the body-fluid of Toxopneustes. 



