494 SUMMARY OF CURRENT RESEARCHES RELATING TO 



putrefactions, and nitrification, in contagious diseases and virulent 

 infections, and in surgical lesions. The author thus sums up " the 

 actual state of our knowledge upon the Bacteria : — 



1. The Bacteria are cellular organisms of vegetable nature. 



2. Their organism is more complicated than was for a long time 

 believed. The principal points brought to light are : their structure, 

 the presence of cilia, the nature of the substances contained in their 

 protoplasm, coloured granules, grains of sulj)hur, &c. 



3. The forms of torula, zooglcea, leptothrix, mycoderma, &c. 



4. The multiple affinities of the Bacteria, on the one hand with the 

 algfe, on the other with the fungi, differently understood by authors, 

 and their development, still unknown for the greater number of 

 species, make it impossible to classify these beings except in a 

 provisional manner. 



5. This development, well studied in several species of Bacillus, 

 has proved that bacteria may multiply not only by fission, but also by 

 formation of spores, and even by veritable sporangia. 



6. These spores or permanent germs are the principal means by 

 which these inferior organisms are disseminated. 



7. As to their role in fermentations, in putrefactions, in contagious 

 diseases, and in surgical lesions, notwithstanding the considerable 

 number of labours of which the Bacteria have been the object in these 

 different points of view, it is not yet possible to define it in a certain 

 manner." 



In concluding the historical part of the book, the author adds that 

 " in presence of these opinions, so diverse, as to the nature of the 

 Bacteria and their classification, we will finish by saying with 

 Cohn :— 



" So long as the makers of Microscopes do not place at our 

 disposal much higher powers, and, as far as possible, without im- 

 mersion, we shall find ourselves, in the domain of the Bacteria, in the 

 situation of a traveller who wanders in an unknown country at the 

 hour of twilight, at the moment when the light of day no longer 

 suffices to enable him clearly to distinguish objects, and when he is 

 conscious that, notwithstanding all his precautions, he is liable to lose 

 his way," 



Not the least valuable part of the book is the thirty-two pages of 

 Bibliography, commencing with Leeuwenhoek's ' Opera Omnia,' of 1772, 

 and ending with a list of more than fifty-two jiapers, published in 

 1880. 



Reproduction of the Bacteria. — The physical teacher, in order to 

 convey to his pupil an idea of distance in the universe, surprises him 

 with calculations of the number of centuries that it would take for 

 a railway train or a cannon ball to traverse the given space. The 

 following calculations, given by Cohn, apply the same idea to a 

 biological question : — 



" Let us suppose, " says Cohn, " that a bacterium divides into two 

 in the space of an hour, then in four at the end of a second hour, 

 then in eight at the end of three hours, in twenty-four hours the 

 number will already amount to more than sixteen millions and a half 



