26 PARASITIC AMOEBA OF MAN. 



It is uncertain just what occurs during the conjuga- 

 tion of organisms of this class, but it is probable that 

 it leads to a rejuvenescence of the vital processes 

 rather than that it is a process of fertilization. 



RESISTANCE TO PHYSICAL CONDITIONS AND CHEM- 

 ICAL AGENCIES. Some species of free-living amoebae 

 are able to withstand a considerable degree of heat 

 and cold, but the parasitic amoebae of man become 

 motionless, as a rule, after exposure for an hour to 

 temperatures below 75 F. It has been suggested by 

 some authorities that the species living in man can 

 be best distinguished from free-living forms by their 

 lesser resistance to heat and cold, the free-living 

 forms remaining motile when exposed to great varia- 

 tions in temperature, while the parasitic amoebae are 

 only motile at a temperature near that of the human 

 body. The writer does not believe that this method 

 of differentiation is of much value, as he has fre- 

 quently observed amoebae, belonging to the genus 

 Entamceba, moving about on a microscopic slide at 

 a temperature far below that to which they are 

 accustomed in the human intestine. Harris and Mus- 

 grave have shown that a temperature of F. is 

 not sufficient to kill some amoebae, but it should be 

 remembered that only the encysted forms are capable 

 of withstanding such low temperatures. 



As regards the resistance of these organisms to 



