316 SEX IN MICROORGANISMS 



calkinsi I) stain deeply (Metz, unpublished) with azo-carmine G 

 (Monne and Slautterback, 1951), and up to 10 per cent of the Kjel- 

 dahl nitrogen may appear as free amino nitrogen (standard formol 

 titration) in such animals, a value which compares favorably with 

 that for alcohol-killed control animals (Metz, unpublished). Evi- 

 dently, then, the amino groups of formalin-killed, reactive animals 

 are not bound to any appreciable extent. 



Possible action of periodate on P-hydroxy amino acid residues 

 (Edsall, 1942) has not been investigated, but apparently hydroxyl 

 groups of carbohydrates are not essential (P. calkinsi I), for animals 

 retain reactivity at periodate concentrations which render them 

 strongly positive to Schiff' s reagent. 



The failure of several organic solvents to remove or destroy 

 mating substance activity (Table V; Metz and Fusco, 1949) would 

 seem to eliminate loosely bound fat-soluble substances as essential 

 constituents. However, Chargaff's (1944) report that alcohol splits 

 lipoprotein, whereas various other solvents do not, is of some inter- 

 est, for this agent destroys mating reactivity even at low concentra- 

 tions (Metz, 1946; Metz and Fusco, 1949; Hiwatashi, 1950). 



Although a large number of agents have been examined for 

 inactivating action on the mating-type substances of Paramecium, 

 only two of these have shown clear-cut differential action on com- 

 plementary mating types. These agents are formalin and nitrous acid. 

 Formalin-killed type II P. calkinsi never give strong mating reactions 

 regardless of the formalin concentration employed for killing. How- 

 ever, type I formalin-killed animals give intense reactions. On the 

 other hand, type II animals killed with HgCli, picric acid or by 

 lyophilization mate as intensively as similarly treated type I animals 

 (Table V; Metz and Butterfield, 1950). The differential action of 

 formalin is even more striking in P. caudatnm, for Hiwatashi (1949b) 

 reports that one of the two mating types in each of four different 

 varieties is completely unreactive after formalin killing, whereas the 

 complementary type in each variety gives strong reactions after for- 

 malin treatment. This action of formalin indicates two series of ho- 

 mologous mating types in P. caiidatuvi and suggests the interesting 

 possibility that these two series correspond to the two general mating 

 types established by intervarietal matings (Table II). Unfortunately 

 the data of Gilman and Hiwatashi are insufficient to establish this 

 relationship. Finally, it should be recalled that formaHn has no dif- 



