Studies on the Life History of Protozoa. 443 



degenerated in a different way. The ectoplasmic parts and the 

 micronuclear structures were not affected until the last depression 

 period. 



The first clearly marked period of depression came in July, about 

 six months after the cultures were started. It was characterized 

 by a well-defined reduction in size (down to 109 microns; see 

 Fig, 3), and by vacuolization of the endoplasm while the ecto- 

 plasm did not appear to be much involved. Many of the individ- 

 uals were characterized by great vacuoles similar to those in 

 starved forms, which distorted the body almost out of recognition, 

 in others the nuclei were fragmented into two or three parts, and 

 in all there was a marked 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 abund- 

 ance (see Studies I). As stated in these Studies (III) 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 ineffective 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 continued on the hay diet, all died. These became smaller 

 and smaller, and again gave morphological indications of starva- 

 tion, notwithstanding 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 com- 

 mon as this observation is, it is important in the present connec- 



