RKSISTAV I. TO IIKAT AND COLD. 



mous multitudes prove that their rate of m . 

 (jiiate to meet the demands made upon tin n seri- 



ously impeded by tin- low temperature of the never 



much ;il)o\-c tin- freezing-point, in which they habitually live. 

 The maximum limit of heat which living inaii. r call resist 

 is in* less variable than its minimum limit. Kiiiiin- found 

 that marine Ani'"i were killed wlien the temp.-i. 



reached 35 C. (95 Falir. ), while this was not the case with 

 fresh-water Amu lt , which survived a heat of 5 , i 10, 



C. higher. Ac&\nOf>hry* isi<-)< //"/////' was not killed until the 

 temperature rose to 44 or 45 C. Dldyniiiim * /////A/ is killed 

 at 35 C. ; while another Myxomycete, j3Ethaiiwn\ .^/'//riim, 

 succumbs only at 40 C. 



Cohn (" LJntersuchungen Uber Bacterien," Beitrage zur 

 Biologie der Pflanzen, Heft 2, 1872) has givm the results of 

 a series of experiments conducted with the view of ascertain- 

 ing the temperature at which Bacteria are destroyed \\ 

 living in a fluid of definite chemical composition, and free 

 from all such complications as must arise from the inequalities 

 of physical condition when solid particles other than the / 

 teria coexist with them. The iluid employed contained 0.1 

 gramme potassium phosphate, 0.1 gr. crysialli/ed magnesium 

 sulphate, 0.1 gr. tribasic calcium phosphate, and (.:> gr. am- 

 monium tartrate, dissolved in 20 cubic centimetres of distilled 

 water. If to a certain quantity of this " normal fluid " a sn all 

 proportion of water containing B<t<-t> rt<i was added, the mul- 

 tiplication of the Ii<n'trri<i went on with rapiditv, whether the 

 mouth of the containing flask was oj)en or hermetically closed. 

 Hermetically-sealed flasks, containing porti n> of tin- normal 

 fluid infected with Tldcferta, were submerged in water heated 

 to various temperatures, the flask being carefully shaken, with- 

 out being raised out of the water, during its submerg. 



The result was, that in those flasks which were tliu- MI!J- 

 jected, for an hour, to a heat of 60-62 C. (140M43 Fahr.), 

 the Bacteria- underwent no development, and the fluid re- 

 mained perfectly clear. On the other hand, in similar experi- 

 ments in which the flasks were heated only to 40 or 50 C. 

 (104-122 Fahr.), the fluid became turbid, 'in conv.-iju.-Mee of 

 the multiplication of the J><i<-f> //'*/, in the OOUT86 of from two 

 to three da v s. 



I am in the habit of demonstrating annually, tliat Pa- 

 solution and hay-infusion, after five minute-' boilin r in a '' 

 properly stopped with cotton-wool, reiraiu perfectly clear of 

 living organisms, however long they may be kept. The same 



