THE CONTRACTILE VACUOLE 433 



nately, no method or group of methods has been devised for the identifi- 

 cation of these structures, which is acceptable to all concerned. However, 

 for the protozoan Golgi apparatus it is generally conceded that in most 

 instances it exists as granules, globules, spherules, short rods, or ovoid 

 structures; but there appear to be many exceptions. These bodies reduce 

 certain osmium and silver compounds to the free metals, thereby causing 

 a blackening of the structures which resists bleaching with turpentine 

 and hydrogen peroxide. Most stains commonly used in cytological studies 

 are ineffective, although in some instances neutral red is found to stain 

 some structures which answer other requirements for the true Golgi 

 apparatus. Except for the occasional positive reaction to neutral red, the 

 protozoan Golgi apparatus reacts in a manner practically identical with 

 that of the metazoan Golgi apparatus. 



Nassonov (1924) demonstrated the presence of osmiophilic mem- 

 branes around the vacuoles in Paramecium caudatum, Lwnotus folium, 

 Nassula laterita, Campanella umbellaria, Epistylis gallea, Zoothamnium 

 arbuscula, Vorticella sp., and Chilomonas Paramecium. These membranes 

 he found to be permanent structures, merely collapsing at systole of the 

 vacuole — not disappearing, to be reformed anew during the next period 

 of diastole. In Paramecium the vacuole system was found to consist of 

 a thin-walled reservoir and filling canals, the latter composed of the 

 short injection canal, the ampulla, and the distal section. The distal 

 section Nassonov found to be surrounded by a specially differentiated 

 plasma, from which hypertonic fluid is secreted into the lumen of the 

 canal. This hypertonicity results in the passage of water into the canal, 

 and ultimately into the vacuole. The vacuole wall in Paramecium is 

 considered not to take part in secretion, but to serve only as a temporary 

 reservoir or bladder. In other forms which possess no filling canals, the 

 osmiophilic vacuole wall is considered capable of performing the secre- 

 tory function as well. The formation of small droplets of fluid within 

 this wall was sometimes seen to occur, following partial systole of the 

 vacuole. 



Subsequent observations by Nassonov (1925) on Chilodon and 

 Dogielella necessitated a modification of the original view so as to 

 include conditions which were not observed in the organisms men- 

 tioned in the earlier article. In Chilodon the osmiophilic material appears 

 as a heavy black ring, although this ring is not always complete. If 



