250 BIOLOGY OF THE PROTOZOA 



he concluded that Infusoria die a natural death after a typical life 

 cycle and after a definite number of generations by division. 



The criticism was soon advanced that adverse conditions and 

 bacterial products were responsible for death of his organisms, or, 

 that instead of dying from old age they were slowly killed. There 

 certainly was some justification for this criticism for not only was 

 the covered medium abnormal but the accumulation of bacterial 

 and protozoan products of metabolism might well have been detri- 

 mental, particularly if certain types of bacteria gained supremacy. 

 Woodruff (1911), furthermore, has shown that excretion products 

 of Paramecium are detrimental to Paramecium, and Stylonychia 

 products to Stylonychia, and the implication is that any type, if 

 continued for long intervals in an unchanged medium, will slowly 

 weaken in vitality and ultimately die. 



Such criticisms, continued even to the present time in connection 

 with isolation culture work, do not minimize the value of the 

 splendid contribution of Maupas in these pioneer studies on vitality. 

 The present day scepticism in regard to his general conclusion is 

 based upon diverse results obtained by various experimenters with 

 mass cultures as compared with isolation cultures, the great majority 

 of the latter giving results which confirm Maupas. In these the 

 criticism that an unfit environment gradually killed the organisms 

 has been met by the use of carefully prepared culture media and by 

 daily transfers of the experimental organisms to freshly prepared 

 media. In this manner the undue accumulation of bacteria and 

 their products is prevented while the organisms under observation 

 are never present in large numbers. 



By use of this method of study the life cycles of many different 

 kinds of ciliates have been established and with the exception of 

 the results obtained by Enriques (1913, 1915, 1916), Chatton 

 (1923) and of Woodruff (1908-1921), they all agree in demonstrating 

 a gradually waning vitality and ultimate death of the protoplasm 

 under observation. The method now generally employed is to start 

 with an ex-conjugant, or individual which has just emerged from 

 conjugation and allow it to reproduce by division three times. Four 

 (Woodruff) or five (Calkins) of the eight resulting individuals are 

 then isolated and continued in daily isolation cultures as "pure 

 lines," four or five pure lines to a " series." For vitality comparisons 

 the daily division-rates of all lines of a series are averaged for periods 

 of five days (Woodruff) or ten days (Calkins), and when the cycle 

 is completed the consecutive five- or ten-day division-rates may be 

 plotted to give a graph in which the ordinates represent the average 

 rates of division, the abscissas the consecutive periods. By this 

 method the history of the vitality of the protoplasm under obser- 

 vation is summarized in a graphic and effective manner (Figs. 131, 

 132, 133). 



