SOME PROBLEMS IN THE PHYSIOLOGY OF THE PROTOZOA 291 



products are carbon dioxid and urea (CO(NH 2 ) 2 ), and it has long been 

 assumed upon a priori grounds that a similar result follows combus- 

 tion in Protozoa. Again, there have been but few observations to 

 confirm this supposition. The contractile vacuole was regarded as an 

 excretory vesicle (Unnblase) by Boeck ('47), Rood ('53), Stein ('56), 

 Leydig ('57), Kolliker ('64), and more recently as an excretory organ 

 by Maupas ('83), Rhumbler ('88), Griffiths ('89), Schewiakoff ('94), 

 Delage and Herouard ('96), besides many others. Biitschli 1 believed 

 that it is a pure hypothesis to assume that the vacuole has an excre- 

 tory function other than that of respiration, but Maupas ('83) insisted 

 upon the physiological necessity of such an excretory organ, and cited 

 as an argument the presence of contractile vacuoles in vegetable 

 zoospores, which, having chlorophyl, can presumably make use of all 

 the carbon dioxid formed, and which, therefore, probably make use of 

 the vacuole for secretion. Maupas's argument is offset by the fact of 

 numerous Protozoa which have no contractile vacuoles, and it follows 

 that if these can get rid of their waste organic matters by osmosis, it 

 is quite possible that forms with vacuoles can do the same. Entz ('88) 

 held that the crystals occasionally found in the vacuoles and reser- 

 voirs of different forms are uric acid (Harnconcremente), a supposition 

 which was supported with direct evidence by Griffiths ('89). The lat- 

 ter determined the presence of uric acid in several different types of 

 Protozoa, including the rhizopod Am&ba and the ciliates Paramcecium 

 and Vorticella. A number of animals were placed on a slide under a 

 cover-glass, and killed with alcohol followed by nitric acid. The 

 slide was then gently warmed, and ammonia was introduced. When 

 the experiments were successful, a number of purple prismatic crys- 

 tals of murexide appeared in the contractile vacuoles, showing that 

 uric acid had been present. These results were repeatedly obtained, 

 although the experiments were not always successful, showing, Grif- 

 fiths says, that the vacuole may have some other functions besides 

 secretion. Until this interesting series of experiments is confirmed, 

 however, Griffi ths's results must be inconclusive. If they are confirmed, 

 on the other hand, the following reflection is warranted, and has a sin- 

 gular interest in the present-day problems of biology: "Through all 

 the multitudinous changes," says Griffiths, "that have taken place dur- 

 ing the lapse of ages in the development of the mammalian kidney, we 

 find that the physiological functions are the same as occur in its origi- 

 nal or primitive form, as represented in the Protozoa." 2 



The secretion from the protoplasmic ,body of definite particles of 

 matter, which may or may not have been at some time a part of the 

 animal protoplasm, and which play some further part in the life activi- 



i('88), p. 1452. 2Z*r. V., p. 135. 



