THE CONTRACTILE VACUOLE 411 



isms, as much of the evidence impHes, then it would be somewhat un- 1 

 expected if such granules are not to be found distributed generally 

 throughout the Protozoa. MacLennan called attention to the fact that 

 many investigators have demonstrated a more or less solid membrane 

 surrounding vacuoles in a variety of Protozoa, these demonstrations 

 having been made by osmic-acid impregnation. Most of these workers, 

 according to MacLennan, used the warm method of impregnation advo- 

 cated by Nassonov. Hirschler showed that this method tends to produce 

 overimpregnation, resulting in the production of a heavy black band or 

 membrane in what is actually a granular zone. MacLennan found this 

 to be true in the Ophryoscolecidae, while impregnation by the cold 

 method shows this same region to be granular, a condition which can be 

 seen in living material. He further calls attention to the fact that figures 

 showing solid impregnation of the vacuolar walls of Chilodon and 

 Dogielella, published by Nassonov, of Balantidium by Bojewa-Petms- 

 chewskaja, and of the Cyclopostheiidae by Strelkow, indicate a marked 

 granular roughening of the outer margin of the osmiophilic layer. He 

 takes this to indicate that what has been interpreted by these authors as 

 a solid membrane may, in fact, be only the result of overimpregnation 

 of a granular zone. Among the Ophryoscolecidae alone MacLennan found 

 various degrees of aggregation of these granules — from virtually none to 

 a very pronounced aggregation — around the contractile vacuole. He fur- 

 ther showed that localization of the origin of contractile vacuoles in these 

 forms is correlated with the degree of aggregation of the granules. 



Of interest in this connection are the observations of Lloyd and Scarth 

 (1926) on the origin of vacuoles in Spirogyra. These authors found that 

 in suflficiently high concentrations even the most innocuous plasmolytes 

 may by themselves cause subsidiary vacuoles to arise in the cytoplasm. It 

 is not only by plasmolytes that this effect is produced however, but also 

 by other more readily penetrating substances such as the narcotics, chloro- 

 form, and ether, and by very low concentrations of salts. But without 

 any artificial influence, similar vacuoles may form in normal cells. Their 

 constant occurrence was demonstrated in the gametes during conjugation 

 in Spirogyra, and their excretory function in the taking up of water from 

 the central vacuole and its discharge to the exterior in typical "contrac- 

 tile" fashion was proved. The authors state that these vacuoles originate 

 from peculiar "lecithin-like" bodies already present in the cytoplasm. 



