90 



Tilgli angle, and in the use of a powerful substage condenser 

 (Abbe's), used without any diaphragm, so that the object shall 

 be lighted up by an intense glare of light. I must confess- 

 that when I first heard of this mode of showing stained Bacteria 

 I felt that if anyone had asked me " How not to do it?" I 

 should probably have suggested some such mode of illumina- 

 tion. A practised microscopist is very fussy about his illumina- 

 tion : he works with but little light — ^just sufficient to bring out 

 details, and no more. He stops out the light by diaphragms, 

 Dallinger's best work was done under an illumination in which 

 all the light passed through a mere pinhole, and I have no 

 doubt that many microscopists have been deterred from fol- 

 lowing Koch's directions by a desire to preserve the details of 

 the picture, all of which are lost under strong illumination. 

 But on further study we find that this is the great object Kocb 

 has in view. Finding in practice that Bacteria stain much 

 deeper than other structures in aniline dyes, he reasoned that 

 if all the objects that are less deeply stained could be blotted 

 out, or rather, dazzled out of the picture, and nothing remain 

 in yiew but the darker colour picture of the deep- stained Bac- 

 teria and a few other objects not likely to be mistaken for 

 them, it would be possible to distinguish these, although in a 

 less illumined field they could not be picked out from other 

 objects in view. General experience has proved that he i» 

 right. 



I shall not ask you to burden your memories with the tire- 

 some details of classification, but it is necessary for our purpose 

 that we bear in mind that in disease there are at least four 

 distinct forms of Bacteria to be recognised — (1) There is the 

 minute rounded body — the micrococcus, existing either separately 

 or in chains ; (2) the short cylindrical cell — the bacterium 

 proper ; (3) the longer and more filamentous cylindrical cells, 

 either isolated or in chains — the bacillus ; and (4) spiral undu- 

 lating filaments — the vibrio and spirillum. It is probable that 

 in their stages of development some of these pass through dif- 

 ferent forms ; but our knowledge on this subject is incomplete. 

 In bringing to your notice the association of some of these 

 bodies with disease we will begin with one of the most simple. 



Let us take a common acute abscess. Dr. Odgston shall be 

 our guide. This gentleman found that a small drop of matter 

 from an acute abscess, when dried on a slide, stained and ob- 

 served after Koch's method, presents to view an immense num- 

 ber of micrococci scattered about the field. When a minute 

 portion of such matter was inoculated into a second and healthy 

 animal, abscesses formed in this second subject, and the pus 

 in these was also loaded with micrococci. A third animal 

 inoculated from the second showed the same results, and 



