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A Normal Periodic Reorganization Process Without Cell Fusion in Paramaecium

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A Normal Periodic Reorganization Process Without Cell Fusion in Paramaecium A NORMAL PERIODIC REORGANIZATION PROCESS WITHOUT CELL FUSION IN PARAMAECIUM LORANDE LOSS WOODRUFF AND RHODA ERDMANN Osborn Zoological. Laboratory, Yale Unicersity SIXTY-SIX FIOUREB (FOUR DOUBLE COLORED PLATES) CONTENTS I. Introduction.... .............. ... .. ............ .. .......... ........ 426 11. Material and methods.. .. :. .. .. .. .. 432 A. Method of conduction of main Culture I.. 432 B. Method of conduction of Subculture IE.. 434 111. Description of the cytological changes in the reorganization process. 436 A. Descending phase ..... .. .. ........... .............. ...... 436 1. Macronucleus.. , . , , , . ,437 2. Micronucleus., , . , . , . , . , , . 440 B. Climax ._........... .. .. ._...... .. .. ... ..... .. ...... .. ....... 443 C. Ascending phase ...... .. .. .. .... ... .. .. .. .... .. .. .. ... .. 450 IV. Cytological details of series of pedigreed cells in the reorganization process. .... .... ...__...... .. ..... .. .. ........... .. .. .. ..... 457 A. Series of cells from Line VI.. .. .. .. 458 B. Series of cells from Lines I to V.. 469 V. The reorganization process in this race after conjugation, and in other races and species of Paramaecium.. ._.. .. 473 VI. The reorganization process and its relation to rhythms,. 476 VII. The reorganization process and its relation to depression periods.. 481 VIII. Endomixis and its relation to conjugation.. 489 IX. Endomixis and its relation to parthenogenesis. ............ .. .. ..... 492 X. Endomixis and its relations to variation, heredity and the significance of conjugation. ........... .. ..................................... 494 Literature cited.. .. .. .. 498 Explanation of plates.. , . , . , . , , . 503 I. IXTRODUCTIOK The conception of the Protozoa as primitive animals has led to innumerable studies on these forms-morphologists and phy- siologists alike being animated with the idea that here many of the riddles of'life propounded by the so-called higher animals would be presented in a simple form and so be more readily solved. While this view of the Protozoa is undoubtedly true $35 THE JOURNAL OF EXPERIMENTALZO~LOOY, VOL. 17, NO. 4 NOVEYBER, 1914 426 LORANDE LOSS WOODRUFF AND RH. ERDMANN in a broad sense, recent studies on these organisms have only served to emphasize that size and simplicity do notnecessarily go hand in hand and that a unicellular or non-cellular animal with all its varied life processes performed within the confinea of a protoplasmic unit presents difficulties which differ in kind rather than in degree from those encountered in the metazoa. No better instance of the truth of this could be presented than that afforded by studies on the life history of the Infusoria. Dujardin's ideas of simplicity-brought forward to combat Ehren- berg's mistaken interpretations of the complexities which he observed-gradually were displaced by the revelations of Bal- biani, Biitschli, Engelmann, Maupas, Hertwig and others on the complicated phenomena of conjugation, while the results of more recent work on conjugation from the standpoint of dynamics and heredity have only served to emphasize the intricacies of the infusorian life processes. The present study fully describes still another complex nuclear phenomenon1 which we have dis- covered in the life of Paramaecium aurelia and which we believe affords the key to certain apparent contradictions in recent results on the life history of the Infusoria. The problems of protoplasmic senescence and the significance of fertilization have afforded the stimulus for a long series of investigations on the life history of Infusoria since, more than three-quarters of a century ago, the leading students of micro- scopic organisms, Ehrenberg and Dujardin, theorized on the potential immortality of these forms. It remained, however, for Biitschli ('76) and Engelmann ('76) to attack the problem experimentally, in the light of zoological advance in the inter- vening years, and to reach the conclusion that continued repro- duction by division results in degeneration and death; while the classic studies by Maupas ('89) on the life history of a number of different species of Infusoria afforded such a wealth of evi- dence pointing in the same direction that conjugation as a sine 1 We have already given brief outlines of this process in the Proc. of thesociety for Exper. Biol. and Med., vol. 11, no. 3, February 18, 1914, and in Biol. Cent., Bd. 34, 1914. In the latter several errors are present owing to the war prevent- ing a revision of proof. PERIODIC REORGANIZATION IN PARAMAECIUM 427 qua non for the life of the Infusoria seemed to be placed upon a firm empirical basis. A series of careful investigations by R. Hertwig (’00-04) and Calkins (’02-’04) confirmed Maupas’ general conclusion that In- fusoria after a more or less definite number of divisions degen- erate and finally die if conjugation is prevented. Further, the latter author found that artificial stimuli of different kinds may be substituted with success for conjugation since by the oppor- tune use of artificial stimulation he was able to prolong the life of one culture of Paramaecium caudatum to the 742d gener- ation. This significant discovery that the death of infusorian cul- tures, bred on a more or less constant medium of hay infusion, may be temporarily deferred by artificial means was corroborated by Woodruff (’05). Enriques (’03) studied the same general problem and reached the conclusion that the degeneration and death observed by Calkins and others was due to the presence of bacterial poisons in view of the fact that he succeeded in breeding Glaucoma scintillans for 683 generations without signs of degeneration when this factor was eliminated. Although Enriques’ interpre- tation of the cause of degeneration in Calkins’ cultures is open to question, the significant fact remains that he kept his ani- mals nearly twice as long as did Maupas or Calkins without conjugation or artificial stimulation, thus suggesting that degen- eration is not inevitable, and that if suitable conditions are supplied reproduction by division can proceed indefinitely The problem was attacked from another point of view by Woodruff (1907 to date) who investigated the possibility that the degeneration observed in the previous investigations was induced by too great uniformity in the conditions of culture, or by the culture medium being deficient in something essential for the continued well-being of the organisms. A race of Para- maecium aurelia (I) was isolated and bred on infusions of various materials found in the natural environment of the animal, while a sub-culture was subjected to the relatively constant hay in- fusion culture conditions employed by Calkins (’04). The result was that the cells bred in the constant hay infusion medium died 428 LORANDE LOSS WOODRUFF AND RH. ERDMANN out after a typical Calkins cycle, while those bred on the ‘varied environment’ medium did not pass through periods of marked physiologica’ depression or show morphological changes which could be interpreted as abnormal. This race is still (June, 1914) in a normal condition, having attained over 4500 generations without conjugation or the use of artificial stimuli. The success with the varied culture medium naturally led to the question whether the longevity of Paramaecium on a varied environment is dependent upon intrinsic stimuli from the fre- quent changes of the medium, or whether a constant medium of hay infusion is unfavorable because it lacks some elements which are essential for the continued existence of the organism. Ac- cordingly, Woodruff and Baitsell (’11 a) bred a sub-culture of this race for a period of nine months on a constant culture medium of beef extract. The continued health of the organisms on this constant medium throughout the experiment, which was continued sufficiently long to include a Calkins cycle if such was inherent, indicated that it is the composition of the medium rather than the changes in the medium which is conducive to the unlimited development of this’ race without the necessity of conjugation or artificial stimulation. From a study of various species of hypotrichous Infusoria, as well as his main culture of Paramaecium aurelia, Woodruff found that minor periodic rises and falls of the division rate occur from which recovery is autonomous. He termed these fluctuations ‘rhythms’ and contrasted them with the so-called cycle, which comprises a varying number of rhythms and, ac- cording to Maupas and Calkins, ends in the death of the race if conjugation or artificial stimulation is not resorted to. The problem of the rhythms was‘ studied intensively by Woodruff and Baitsell (’11 b) who showed that when Paramaecium aurelia is subjected to the most constant environmental conditions it is impossible to eliminate the rhythm and thus resolve the graph of the multiplication rate into an approximately straight line. Accordingly there are inherent rhythmical changes in the phe- nomena of the cell which produce slight changes of the divis’on rate. The same result was reached by Woodruff and Baitsell PERIODIC REORGANIZATION IN PARAMAECIUM 429 (’11 c) from a study of the temperature coefficient of the rate of reproduction of this culture which showed that the rate of cell division of Paramaecium is ivfluenced by the temperature at a velocity similar to that for a chemical reaction-except when the rhythms interfere. The results from the study of this pedigreed race of Para- niaecium aurelia have led WooW to conclude that this organ- ism, when subjected to suitable culture conditions,
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