310 SEX IN MICROORGANISMS 



son, 1950) and by Metz and Pitelka (unpublished) in lyophilized 

 preparations of P. calkinsi (Plate I). The last study is the only 

 serious visual attempt that has so far been made to detect mating-type 

 differences in paramecium cilia. The material was prepared for elec- 

 tron microscopy in several ways including drying living and formahn- 

 killed paramecia in air and lyophilizing living and formalin-killed ani- 

 mals directly to the collodion membrane. Comparisons were then 

 made among (1) cilia of animals from reactive and unreactive cul- 

 tures, (2) cilia from reactive animals of the two complementary 

 mating types, and (3) ciha of control animals with others that had 

 been removed from mating reaction agglutinates. These comparisons 

 revealed no consistent differences within the three categories. These 

 observations thus confirm the original supposition, namely, that the 

 mating-type substances constitute part of the molecular pattern of the 

 cilium surface membrane. No evidence was obtained for an extra- 

 cellular coat or capsule about the cilium. The tips of the cilia like- 

 wise showed no specialized organization. However, a sharp reduction 

 in diameter was observed approximately 1 micron from the cilium 

 tip. This narrow terminal part of the cilium is evidently more deli- 

 cate than the remainder of the organelle, since it was distorted in 

 many of the preparations. 



Chemistry of the Mating-Type Substances. A proper chemical 

 study of the mating-type substances should reveal the general chem- 

 ical nature of these substances. Furthermore it might be expected to 

 demonstrate specific differences between complementary substances. 

 Such differences might account for the specificity of the mating 

 reaction and provide some information about the manner of inter- 

 action of these agents. 



Ordinarily, characterization of substances of biological origin is 

 achieved by appropriate extraction and purification followed by an 

 identification and description based on physical and chemical proper- 

 ties. A number of different physical and chemical agents have been 

 employed in attempts to extract mating substances from paramecia. 

 They include breaking up the reactive animals by mechanical means 

 (Metz, 1946; Metz and Butterfield, 1950; Hiwatashi, 1950), by 

 freeze-thawing (Metz, 1946), irradiation with x-rays (Wichterman, 

 1948), heating (Metz, 1946), acid and alkaUne extraction (Metz, 

 1946), digestion with enzymes (Metz and Butterfield, 1950), extrac- 

 tion with salt solutions (Metz, 1946), detergents (Metz, unpub- 



