1922] Hees: The Micro-Injection of I'uramaecium '237 



The vacuole is filled with bacteria ami other food materials whieh 

 ai'e wafted in by the cytopharyngeal membranelles and is then de- 

 tached and passed into the endoplasm by a process whieh resembles 

 a swallowing movement. The food vacuole first becomes tear-shaped 

 by being forced out to a point opposite the attached end. It is then 

 rotated through an angle of 180°, being in the meantime drawn out 

 at the attached end, so that when detached it is spindle shaped, but 

 quickly becomes spherical. 



There is a forward streaming of the endoplasm and its inclusions 

 along the animal's left side from the posterior to the anterior end 

 and caudad along the right side. The food vacuole begins this circuit 

 but goes only halfway, crossing over at a point opposite the po.sterior 

 end of the macronucleus and returning in the posteriorly streaming 

 protoplasm of the right side to the starting point. It usually repeats 

 this circuit several times. 



It was demonstrated by the use of very dilute solutions of neutral 

 red that the reaction of the vacuole when first released from the cyto- 

 pharynx is acid. During this time endoplasmic granules, whieh at 

 fii>;t adhere to the vacuolar membrane, pass through the latter into 

 the vacuole. They are also stained red. These granules and the 

 ingested organisms are then aggregated into a compact mulberry 

 ma.ss, surrounded by a clear fluid within the vacuole. The fluid is 

 gradually resorbed, so that the vacuole becomes .smaller until its 

 membrane comes into inuuediate contact with the mulberry mass. 

 Then the vacuole begins to get larger, the mulberrj' mass is disrupted, 

 and the endoplasmic granules and the bacteria become again sharply 

 differentiated. This marks the close of the first period. 



The microorganisms within tlie vacuole and the vacuolar fluid now 

 become colorless. The granules ntain their color until finally dis- 

 solved. These changes charaeterizi' a transition from an acid to 

 an alkaline reaction. No further changes were recorded until the 

 vacuoles become aggregated in the region of the anal aperture and 

 are defaeeated. 



Nirenstcin concluded, in agreement with Greenwood (1894), and 

 Greenwood and Saunders (1894), and in opposition to Metehnikoff 

 (1889), that uo digestion takes place during the time of the acid 

 reaction. But Metalnikow (1912) found that the acid reaction con- 

 tinues longer and is more pronounced when protein is fed to Para- 

 maccium than when carbohydrates are fed. Lund (1914) proved that 

 in Bursari'd protein digestion occurs during the acid reaction. 



