JOURNAL 



OF THE 



ROYAL MICROSCOPICAL SOCIETY. 



FEBKUAKY, 1880. 



TKANSACTIONS OF THE SOCIETY. 



I. — 0)i a Series of Experiments made to determine the Thermal 

 Death-])oint of hnoivn Monad Germs when the Heat is endured 

 in a Fluid. By the Kev. W. H. Dallingek, F.E.M.S. 



(Read 10th December, 1879.) 



Plates I. and II. 



In a group of papers on " The Life-Histories " of a series of well- 

 marked monad forms, read before this Society between the years 

 1873 and 1876,* it was shown that in every instance when the 

 organism was steadily followed in its developmental history, its 

 vital continuity as a distinct form was secured by a process which 

 was, without doubt, the practical equivalent of a genetic one. 



In the set of observations here referred to six monads — quite 

 distinct in all respects — varying in their longest diameter from the 

 ? AiT of ^^ m.Qh. to the toVo of an inch, were carefully followed from 

 their ordinary condition, through a series of well-observed changes, 

 into a condition in which slightly dissimilar states of the same form 

 blended, becoming a stiU sac. This sac, it was shown, in every caso 

 ultimately emitted germs — exquisitely minute semi-opaque atoms 

 — in enormous multitudes. But in one instance these were so 

 minute as, at first, to defy disclosure by our finest and most 

 powerful optical aids, however carefully employed, and the demon- 

 stration of the existence of germs in this case was only effected by 

 watching a space over which the apparently glairy fluid that had 

 poured forth from the sac had passed ; and then by repeated obser- 

 vation it was seen that what in the issue proved to be germs, did 

 arise, being then of the apparent size of the least of the germs of 

 the other monads whose sac-contents were at once shown to be 

 such. But they were not in the same condition as these, that 

 being always semi-opaque, while these, when they appeared, had a 

 slightly yellowish tint and were transparent, and when persistently 



* 8eo ' Monthly Microscopical Journal,' vols, x.-xiii. 

 VOL. III. B 



