14 THE ANATOMY OF INVERTEBRATED ANIMALS. 



holds good for a solution analogous to Cohn's, but in which 

 all the saline ingredients are ammonia salts ; ' and in which 

 Bacteria nourish luxuriantly. Prof. Tyndall's large series 

 of experiments give the same results for fluids of the most 

 diverse composition. The cases of milk and some other fluids 

 in which Bacteria are said to appear, after they have been 

 heated above the boiling-point, require renewed investigation. 



Both in Ktihne's and in Cohn's experiments, which last have 

 lately been confirmed and extended by Dr. Roberts, of Man- 

 chester, it was noted that long exposure to a lower temper- 

 ature than that which brings about immediate destruction of 

 life produces the same effect as short exposure to the latter 

 temperature. Thus, though all the Bacteria were killed, with 

 certainty, in the normal fluid, by short exposure to temper- 

 atures at or above 60° C. (140° Fahr.), Cohn observed that, 

 when a flask containing infected normal fluid was heated to 

 50°-52° C. (122°-125° Fahr.) for only an hour, the conse- 

 quent multiplication of the Bacteria was manifested much 

 earlier than in one which had been exposed for two hours to 

 the same temperature. 



It appears to be very generally held that the simpler vege- 

 table organisms are deprived of life at temperatures as high 

 as 60° C. (140° Fahr.) ; but it is affirmed by competent ob- 

 servers that Algce have been found living in hot springs at 

 much higher temperatures, namely, from 168° to 208° Fahr., 

 for which latter surprising fact we have the high authority of 

 Descloiseaux. It is no explanation of these phenomena, but 

 only another mode of stating them, to say that these organ- 

 isms have become " accustomed " to such temperatures. If 

 this degree of heat were absolutely incompatible with the 

 activity of living matter, the plants could no more resist it 

 than they could become " accustomed " to be being made red- 

 hot. Habit may modify subsidiary, but cannot affect funda- 

 mental, conditions. . 



Recent investigations point to the conclusion that the im- 

 mediate cause of the arrest of vitality, in the first place, and 

 of its destruction, in the second, is the coagulation of certain 

 substances in the protoplasm, and that the latter contains 

 various coagulable matters, which solidify at different temper- 

 atures. And it remains to be seen how far the death of any 

 form of living matter, at a given temperature, depends on the 



i These were as pure as I could obtain them. It is possible the fluid may 

 have contained an infinitesimal proportion of fixed mineral matter, 



