30 JOURNAL OF THE TRINIDAD 



Before noticing the genera mentioned in this table a few 

 remarks may be made on some practical points connected with 

 bacteria. 



One of the most interesting and important of these is the 

 question of pleomorphism. 



In Cohn's first classification mentioned above he divided 

 bacteria into four groups : 



1. Sphsero-bacteria ; globules (micrococcus.) 



2. Micro-bacteria ; short rods (bacterium.) 



3. Desmo-bacteria ; long rods (bacillus and vibrio. ) 



4. Spiro-bacteria ; spirals (spirochete and spirillum.) 



Billroth in 1874 opposed this division and went to the other 

 extreme. He regarded all Cohn's forms as developmental forms 

 of one micro-organism which he called Coccobacteria septica. 



In 1875 Colin answered Billroth, still maintaining that 

 distinct genera and species existed. He produced a second 

 classification, placing the bacteria under a new group, the 

 Schizophytes, and adding several genera. 



Oar present knowledge admits a mean between the extreme 

 views of Cohn and Billroth. We now accept the doctrine of 

 pleomorphism which was to some extent anticipated by Lister in 

 1873 after observations on a bacterium in milk, but was first 

 definitely formulated by Lankester in the same year after his 

 researches on beggiatoa to be referred to later. He says : " The 

 existence of true species of bacteria must be characterized, not 

 by the simple form features used by Cohn, but by the ensemble 

 of their morphological and physiological properties, as exhibited 

 in their complete life-histories." 



This theory of pleomorphism has since been abundantly 

 confirmed by the researches of Neelsen and Cienkowski on the 

 bacillus of blue milk, of Zopf on beggiatoa and cladsthrix, of 

 Van Tieghem on Clostridium, and of others. It has the merit of 

 being simp'e and at the same time rational. We should not 

 think of separating a fern into two species because the young 

 fronds differ in shape from those of the fully grown plant, nor 

 should we suppose that the common holly contains two species, 

 because the leaves at the base are prickly for purposes of defence, 

 while those at the top of the tree are plain. Neither would 

 anyone imagine that the e irly cotyledons of a plant just emerging 

 from the soil represent a species distinct from the fully developed 

 plant, because the latter shows totally different leaves and stem. 

 And yet, to compare small things with great, those who made the 

 above gross mistakes would not be much more ridiculous than 

 those who tr'ed to divide bacteria by absolute morphological 

 characters. Science is always slow to give narass, and prov;- 



