232 PROGRESS OF MICROSCOPICAL SCIENCE. 



' Pasteur's solution,' and the other a boiled turnip-infusion, and if 

 we place them beneath the same bell-jar, it will be found that the 

 first fluid remains clear and free from Bacteria for an indefinite 

 period, whilst the second invariably becomes turbid in one or two 

 days. 



" What is the explanation of these discordant results ? We have 

 a right to infer that all pre-existing life has been destroyed in each of 

 the fluids ; * we have proved also that such fluids are not usually 

 infected by Bacteria derived from the air ; in this very case, in fact, 

 the putrescible saline fluid remains pure, although the organic in- 

 fusion standing by its side rapidly putrefies. We can only infer, 

 therefore, that whilst the boiled saline solution is quite incapable of 

 engendering Bacteria,^ such organisms are able to arise de novo in 

 the boiled organic infusion. 



" Although this inference may be legitimately drawn from such 

 experiments as I have here referred to, fortunately it is confirmed and 

 strengthened by the labours of many investigators who have worked 

 under the influence of much more stringent conditions, and in which 

 closed vessels of various kinds have been employ ed.J 



"Whilst we may therefore infer (1), that the putrefaction which 

 occurs in many previously boiled fluids when exposed to the air is 

 not due to a contamination by germs derived from the atmosphere, 

 we have also the same right to conclude (2), that in many cases the 

 first organisms which appear in such fluids have arisen de novo, 

 rather than by any process of reproduction from pre-existing forms 

 of life. 



" Admitting, therefore, that Bacteria are ferments capable of initi- 

 ating putrefactive changes, I am a firm believer also in the existence 

 of not-living ferments under the influence of which putrefactive 

 changes may be initiated in certain fluids — changes which are almost 

 invariably accompanied by a new birth of living particles capable of 

 rapidly developing into Bacteria." 



Balanoglossus and Tornaria. — The history of these two interesting 

 creatures is fully given in a recently-published memoir of Professor 

 Agassiz's (published from the Memoirs of the Academy of Sciences, 

 on January 14, 1873). In this memoir, says Professor Verrill, who 

 gives an analysis of it in ' Silliman's American Journal ' for March, 

 Professor Agassiz gives us a nearly complete history of the development 

 of the larva long known as Tornaria, and until recently universally 

 regarded as the larva of an Echinoderm, into the very remarkable worm 

 Balanoglossus. That Tornaria is the larva of this or some allied genus, 

 had been rendered very probable by the observations of MetschnikoflF, 



* [Note, Jan. 31, 1873.]— In 'The Beginnings of Life,' vol. i. p. 332, note 1, 

 I have cited facts strongly tending to show that Bacteria are killed in infusions of 

 turnip or of hay, when these have been heated to a temperature of 140° F. They 

 also seem to die at the same temperature in solutions of amnionic tartrate with 

 sodic phosphate. 



t See ' Beginnings of Life,' vol. ii. p. 35, and vol. i. p. 463. 



X See a recent communication by Prof. Burdon Sanderson, in ' Nature,' January 

 9th, the greater portion of which appeared in 'M. M. J.' for February. 



