LVSnSOMES, A NliW CROt'P Ol' CYTOPLASMIC PAKTICI.IIS 1 47 



results were, however, questioned by Mayershach aiul Pearse(63), who were 

 Luiahle to contirni ihein by nieaus of a histoehemical technique employing 

 Huorescent antibodies. The problem has recently been reinvestigated by 

 Straus (95), who has devised an elegant methotl based on the intra\enous injec- 

 tion of crystalline horse-radish peroxidase and the subsec]uenl assay of the enzyme. 

 A considerable concentration of the injected protein in the droplet fractions could 

 be evidenced in this manner. According to Straus (personal communication), 

 many tissues share this ability to take up circulating peroxidase. That the segre- 

 gated protein may subsequently undergo hydrolysis within the droplets is sug- 

 gested by the results obtained on kidney slices by Oliver, MacDowell and 

 Lee (70). 



In our laboratory Dr. Beaufay has examined the possibility that lysosomes may 

 play a role in the segregation of substances which are specifically concentrated in 

 bile. His results were negative with bromsulfalein and with an iodinated opacify- 

 ing agent (biligraphin), which were recovered almost entirely in the final super- 

 natant of liver homogenates from animals killed 10-30 minutes after the intraven- 

 ous injection of these compounds. With neutral red, on the other hand, part of 

 the dye was retained in the particulate fractions, the highest concentration being 

 found in the fraction richest in lysosomes. This finding is in agreement with the 

 statement by Brachet (16) that lysosomes may be identical with the vacuoles which 

 can be demonstrated by staining cells in vivo with basic dyes ( neutral red, 

 toluidine blue). Whether the phenomenon is a specific one remains to be verified, 

 since the control experiment of adding the dye to a homogenate was not per- 

 formed. On the other hand, it is also possible that the negative results mentioned 

 above may be due to an insufficient time lapse between injecting and killing the 

 animals. In the case of kidney, it is stated by Oliver, MacDowell and Lee (70) 

 that the injected proteins are first diffusely distributed within the cells and torm 

 droplets only after 2-3 hours. 



These various results, especially the well documented observations on kidney 

 droplets, suggest strongly a relationship between lysosomes and engulfing 

 vacuoles, the functional link being presumably provided by the digestive processes 

 taking place within these vacuoles. They do not, however, clarify the nature of 

 this relationship. If, as appears to be the most reasonable assumption, the drop- 

 lets or lysosomes actually contain material taken up by pinocytosis as well as the 

 various enzymes which have been detected within them, we are then left with 

 the problem as to how both types of components actually come to be segregated 

 together. 



It is generally agreed (e.g., 10). that pinocytosis vacuoles are formed from the 

 cell membrane, which folds around a droplet of ambient fluid. Thus and almost 

 by definition, the pinocytosed material may be said to be present within the 

 vacuoles from the time at which they are first formed. That the droplets may 



