The Microscope. 7 



often one end switching about violently, the other nearly quiet, 

 occasionally turning somersaults. I observe comparatively few 

 rapid swimmers. Here are some rods, with one or more nuclear 

 points ; they are individuals thinning off, ready to break up 

 into separate parts; in other mounts we find them lounging 

 lazily or moving more slowly ; they seem to be all of one 

 species, the length depending upon the age. They are light or 

 translucent bodies containing light contents. In further study 

 of them in soft, slimj^, rotten onions, we find a great multitude 

 to be from 3 to 5,v. long and about .75,^ wide. They are light, 

 shadowy little fellows, very difficult to see, much harder to 

 define than the protoplasm itself, whi-jh may, in certain stages 

 of development, be seen with a first-class one-half inch objec- 

 tive; but this bacterium requires finer machinery and more 

 careful handling ; when the light is the very best, they can be 

 seen through a one-fifth, but a one-eighth immersion is decidedly 

 better. They appear either straight or slightly curved, accord- 

 ing, as I believe, to their position in the line of vision ; the 

 number of curved ones would indicate that they are probably 

 all curved. This and their shadow}^ dimness are leading char- 

 acteristics. When they are first removed from the rotting 

 onion (a drop of juice) and mounted in water under a one- 

 eighth, they present a beautiful sight, darting about like a 

 swarm of bees in their narrow space under the cover glass, a 

 grand sight when the}^ are very numerous. After watching 

 them thus for about an hour, they quieted down to their ordin- 

 ary state of activit3\ These specific bacteria are larger and 

 different in form from either Bacterium termo or B. lineola, also 

 very variable, but they are in the same brotherhood. I have 

 no means of knowing certainly' its identity, or whether it is new 

 and undescribed or not, but this is probably the case. I can 

 find no account of it ; for our present use we will name it Bacter- 

 ium refringente. As decomposition of the onion progresses, 

 these bacteria become very numerous. A Micrococcus appears 

 among them, and after about a week the field of the mount from 

 the same onion is filled with large oval bodies, variable in size, 

 an average being about 6 by 8a. These are some unknown 

 species of Micrococcus of large size, appearing at first sight 

 very like mould spores. They possess light contents and a 

 light spore or nucleus in each one, and a very thin cell wall ; 



