128 PROTOPLASMIC AGE OF PROTOZOA 



absence of the larger food granules and gastric vacuoles which 

 characterize the normal animals, and this, notwithstanding the fact 

 that bacterial food was present in abundance (see Studies I). As 

 stated in these Studies (HI), the organisms under these conditions 

 still take food, and in some cases the endoplasm appears opaque with 

 the undigested food balls, but the decrease in size continues and 

 the endoplasmic vacuolization is not prevented by the presence of the 

 food. It is the digestive function, apparently, which becomes ineffec- 

 tive at such periods, and if this is a correct assumption, this function 

 can be stimulated, as I have shown by the experiments. 



''Identical results were obtained in the period of depression in 

 December, 1901, a depression which was again overcome by the use 

 of beef extract, while the individuals of the series which had been con- 

 tinued on the hay diet all died. These became smaller and smaller, 

 and again gave morphological indications of starvation, notwith- 

 standing the fact that the individuals which had been stimulated with 

 the beef extract were living and reproducing normally in the same food 

 medium. They became much reduced in size, the endoplasm became 

 distorted with vacuoles, and they died with absolutely no indication of 

 disease through parasites. 



'These observations show, therefore, that starvation effects may 

 be produced, even though the animals are living in a medium rich in 

 food. It is trite to say that to prevent starvation we must have not 

 only food, but the ability to digest and assimilate it, yet common as 

 this observation is, it is important in the present connection, and 

 involves a factor which cannot be overlooked in any discussion on 

 old age. 



"In the June period, as stated previously, the same conditions were 

 not observed, for the organisms, in part at least, had been treated with 

 the beef extract every week during the first three months, since the 

 previous period of depression. The division rate began to run down 

 in the case of the B series in April, in the A series in May, and in all of 

 the material that had been continued on the beef the characteristic 

 structure was a densely granular endoplasm (Fig. 26, p. 82). In the 

 specimens that had not been treated with the beef since the preceding 

 December this character of the endoplasm was not noted. These 

 unstimulated individuals died out in about the 508th generation (B 

 series) after becoming much emaciated and reduced in size, and with 

 reduced nuclei. . . . The unstimulated A series did not die out 

 until about two weeks later. At the time when the B individual 

 described above died (May 12) the unstimulated A series was char- 

 acterized by somewhat reduced size, a declining division rate, and 

 absence of the dense protoplasmic granules. In the stimulated A 

 series, on the other hand, (Al and A2) of about the 560th genera- 

 tion, the structures were normal, gastric vacuoles were numerous, and 



