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A TEXTBOOK OF PHYSIOLOGY 



of the chromosomes seems guided by the spindle, and the new 

 nuclei are attracted to, and formed in, the neighbourhood of the 

 daughter centrosomes. Some authorities hold this to be as constant 

 and permanent a feature as the division of the chromatin, but recent 

 evidence makes this unlikely. 



Reproduction. The ancients believed that many forms of life, even 

 of such a degree of complexity as the insects, generated spontaneously 

 from slime and similar dead matter. In recent times, the belief in 

 the generation of the animate from the inanimate has been confined 

 to the very lowest forms of life. Such a belief is now dead. It has 

 been conclusively shown that if a nutritive solution, such as milk, be 





FiQ. 4G.8lylonyckia, AM> ENUCLEATED FRAGMENTS. (Redrawn after Verwoi-n.) 



The lines show the planes of section of the entire animal. The middle piece, which 

 contains two nuclei, regenerates an entire animal. The enucleated fragments 

 shown on the right swim for a time and then perish. 



heated for a sufficient time in sealed tubes at a high temperature, 

 such as 200 C., it remains free for all time from all forms of life, and 

 does not putrefy. Life comes only from the living. The explanation 

 of spontaneous generation, which to many has appeared apparent, 

 is that various forms of life, and particularly the spores of bacteria, 

 can withstand moderate heating or drying for a great length 

 of time. Although apparently dead, they become revivified when 

 again put in suitable conditions. Leuwenhoek, the famous Dutch 

 scientist of the seventeenth century, kept in a piece of paper the red 

 dust which he found in the gutter of his roof, and saw the little wheel 

 animal, the rotifer, become active when the dust was wet several 



