1 82 BACTERIOLOGY. 



The belief is nevertheless rapidly gaining ground 

 that the lowest forms of vegetable life cannot be 

 divided by a hard and fast line into a series with 

 chlorophyll (Alga), and a series without it (Fungi), 

 and the tendency now is to solve the difference of 

 opinion between Cohn and Nageli by following the 

 example of Sachs, and amalgamating the two 

 series into one group, the Tkallophytes. 



Researches by competent observers have quite 

 recently clearly demonstrated that several micro- 

 organisms in their life cycle exhibit successively 

 the shapes characteristic of the orders of Cohn. 



This doctrine of pleomorphhm, now widely ac- 

 cepted, was distinctly foreshadowed in a publication* 

 by Lister in 1873, though this memoir contained 

 certain conclusions which have since been aban- 

 doned. Lister described forms of cocci, bacteria, 

 bacilli, and streptothrix in milk, which he regarded 

 as phases of the same micro-organism, JBacterium 

 lactis. As a result of his observations Lister 

 remarks that " any classification of bacteria hitherto 

 made from that of Ehrenberg to that of Cohn based 

 upon absolute morphological characters is entirely 

 untrustworthy." To Lankester, however, belongs 

 the credit of having definitely and precisely formu- 

 lated this doctrine. In a paper, t also published in 

 1873, Lankester observed that the series of form- 

 phases which he had discovered in the case of a 



* Lister, Quart. Journ. Microscop. Sci., 1873, pp. 380 408. 

 f Lankester, Ibid, pp. 408425, and 1876, pp. 278283. 



