1891.] MICROSCOPICAL JOURNAL. 175 



5. Union with Other Cells. — Among the general conditions of the 

 power of cell-reproduction in some cases at least is the necessity of the 

 union of the substance of two cells. This process has been observed in 

 many widely separate instances, thus the egg-cells of animals and plants 

 must be fertilized. Spirogyra, after a certain interval, ceases reproduc- 

 ing by division, and cell union occurs. Amoiba, too, conjugates two 

 amcpbiu fusing into one which then divides, and the products redivide 

 in a lively manner. This interruption in the process of cell divii-ion 

 has, no doubt, great importance, and some biologists are inclined to 

 regard it as the vehicle, one may say, of inheritance, the two elements 

 bringing their diverse traits together, and fusing them to form a single 

 cell partaking of the nature of each, and consequently not absolutely like 

 either. ^ 



6. Summary. — The condition of cell-reproduction may be briefly 

 summarized as : i , nitrogeneous food ; 2, warmth; 3, moisture; 4, oc- 

 casional union of two cells to form one ; 5, light is not primarily neces- 

 sary to cell-reproduction. 



[_To be continued.'] 



Micro-Orgaiiisms.* 



By FLOYD DAVIS, M. Sc, Ph. D., 



DBS MOINES, IOWA. 



People who have never studied nature through a microscope have but 

 little true conception of the real living world around us. The number 

 of plants and animals with which we are familiar through the naked 

 eye is insignificant when compared with the countless myriads of liv- 

 ing bacteria which surround us, and can be seen through a powerful 

 microscope. 



The Dutch naturalist, Antonius Van Loenwenhoeck, as early as 1675, 

 observed and studied bacteria, but our knowledge of these micro-or- 

 ganisms has been mostly attained during the last thirty years. In 1848 

 Fuchs observed these minute bodies in animals dead from septic infec- 

 tion, and in 1849 and 1S50 Branell and Davaine observed them in the 

 blood of sheep dead from anthrax ; but no eflbrts seem to have been 

 made to establish any genetic relation between bacteria and disease 

 until Pasteur's work on Fermentations appeared in 1861. Since that 

 date, remarkable and interesting discoveries in bacteriology have been 

 made by Pasteur, Koch, Klebs, Cohn, Virchow, Burdon, Sanderson, 

 Tyndall, and many others, from whom we have been given convincing 

 proof of the validity of the " germ theory of disease." . 



It is now almost universally admitted that bacteria, or microbes, be- 

 long to the domain of botany, and are the simplest and minutest organ- 

 isms in the vegetable kingdom. The great majority of these micro- 

 organisms are harmless to the human system, and are beneficent agents 

 in nature ; but some of them are infectious, the diseases that they pro- 

 duce being called zymotic, in consequence of their course resembling 

 a process of fermentation. Such diseases as cholera, typhoid fever, 

 diphtheria, scarlet fever, and erysipelas belong to this class. 



As long as the cause of these diseases was undetermined, the science 



*From Potable h^'aUr hy permission of Messrs. Silver, Burdett & Co., publisliers, New York. 



